cache refresh does not work
```
3|datasets | DEBUG: 2021-12-14 14:52:48,994 - worker - job assigned: 61b8afbff18404b0ff26d942 for dataset: Babelscape/wikineural
3|datasets | INFO: 2021-12-14 14:52:48,994 - worker - compute dataset 'Babelscape/wikineural'
3|datasets | DEBUG: 2021-12-14 14:52:50,391 - worker - job finished: 61b8afbff18404b0ff26d942 for dataset: Babelscape/wikineural
3|datasets | Traceback (most recent call last):
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/mongoengine/document.py", line 407, in save
3|datasets |     object_id = self._save_create(doc, force_insert, write_concern)
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/mongoengine/document.py", line 472, in _save_create
3|datasets |     object_id = wc_collection.insert_one(doc).inserted_id
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 705, in insert_one
3|datasets |     self._insert(document,
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 620, in _insert
3|datasets |     return self._insert_one(
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 609, in _insert_one
3|datasets |     self.__database.client._retryable_write(
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/mongo_client.py", line 1552, in _retryable_write
3|datasets |     return self._retry_with_session(retryable, func, s, None)
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/mongo_client.py", line 1438, in _retry_with_session
3|datasets |     return self._retry_internal(retryable, func, session, bulk)
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/mongo_client.py", line 1470, in _retry_internal
3|datasets |     return func(session, sock_info, retryable)
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 607, in _insert_command
3|datasets |     _check_write_command_response(result)
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/helpers.py", line 241, in _check_write_command_response
3|datasets |     _raise_last_write_error(write_errors)
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/helpers.py", line 210, in _raise_last_write_error
3|datasets |     raise DuplicateKeyError(error.get("errmsg"), 11000, error)
3|datasets | pymongo.errors.DuplicateKeyError: E11000 duplicate key error collection: datasets_preview_cache.datasets index: dataset_name_1 dup key: { dataset_name: "Babelscape/wikineural" }, full error: {'index': 0, 'code': 11000, 'keyPattern': {'dataset_name': 1}, 'keyValue': {'dataset_name': 'Babelscape/wikineural'}, 'errmsg': 'E11000 duplicate key error collection: datasets_preview_cache.datasets index: dataset_name_1 dup key: { dataset_name: "Babelscape/wikineural" }'}
3|datasets |
3|datasets | During handling of the above exception, another exception occurred:
3|datasets |
3|datasets | Traceback (most recent call last):
3|datasets |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/worker.py", line 92, in <module>
3|datasets |     loop()
3|datasets |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/worker.py", line 81, in loop
3|datasets |     while not has_resources() or not process_next_job():
3|datasets |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/worker.py", line 43, in process_next_job
3|datasets |     refresh_dataset(dataset_name=dataset_name)
3|datasets |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/io/cache.py", line 239, in refresh_dataset
3|datasets |     upsert_dataset(dataset)
3|datasets |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/io/cache.py", line 186, in upsert_dataset
3|datasets |     DbDataset(dataset_name=dataset_name, status="valid").save()
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/mongoengine/document.py", line 430, in save
3|datasets |     raise NotUniqueError(message % err)
3|datasets | mongoengine.errors.NotUniqueError: Tried to save duplicate unique keys (E11000 duplicate key error collection: datasets_preview_cache.datasets index: dataset_name_1 dup key: { dataset_name: "Babelscape/wikineural" }, full error: {'index': 0, 'code': 11000, 'keyPattern': {'dataset_name': 1}, 'keyValue': {'dataset_name': 'Babelscape/wikineural'}, 'errmsg': 'E11000 duplicate key error collection: datasets_preview_cache.datasets index: dataset_name_1 dup key: { dataset_name: "Babelscape/wikineural" }'})
3|datasets | make: *** [Makefile:38: worker] Error 1
```
cache refresh does not work: ```
3|datasets | DEBUG: 2021-12-14 14:52:48,994 - worker - job assigned: 61b8afbff18404b0ff26d942 for dataset: Babelscape/wikineural
3|datasets | INFO: 2021-12-14 14:52:48,994 - worker - compute dataset 'Babelscape/wikineural'
3|datasets | DEBUG: 2021-12-14 14:52:50,391 - worker - job finished: 61b8afbff18404b0ff26d942 for dataset: Babelscape/wikineural
3|datasets | Traceback (most recent call last):
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/mongoengine/document.py", line 407, in save
3|datasets |     object_id = self._save_create(doc, force_insert, write_concern)
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/mongoengine/document.py", line 472, in _save_create
3|datasets |     object_id = wc_collection.insert_one(doc).inserted_id
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 705, in insert_one
3|datasets |     self._insert(document,
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 620, in _insert
3|datasets |     return self._insert_one(
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 609, in _insert_one
3|datasets |     self.__database.client._retryable_write(
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/mongo_client.py", line 1552, in _retryable_write
3|datasets |     return self._retry_with_session(retryable, func, s, None)
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/mongo_client.py", line 1438, in _retry_with_session
3|datasets |     return self._retry_internal(retryable, func, session, bulk)
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/mongo_client.py", line 1470, in _retry_internal
3|datasets |     return func(session, sock_info, retryable)
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 607, in _insert_command
3|datasets |     _check_write_command_response(result)
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/helpers.py", line 241, in _check_write_command_response
3|datasets |     _raise_last_write_error(write_errors)
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/helpers.py", line 210, in _raise_last_write_error
3|datasets |     raise DuplicateKeyError(error.get("errmsg"), 11000, error)
3|datasets | pymongo.errors.DuplicateKeyError: E11000 duplicate key error collection: datasets_preview_cache.datasets index: dataset_name_1 dup key: { dataset_name: "Babelscape/wikineural" }, full error: {'index': 0, 'code': 11000, 'keyPattern': {'dataset_name': 1}, 'keyValue': {'dataset_name': 'Babelscape/wikineural'}, 'errmsg': 'E11000 duplicate key error collection: datasets_preview_cache.datasets index: dataset_name_1 dup key: { dataset_name: "Babelscape/wikineural" }'}
3|datasets |
3|datasets | During handling of the above exception, another exception occurred:
3|datasets |
3|datasets | Traceback (most recent call last):
3|datasets |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/worker.py", line 92, in <module>
3|datasets |     loop()
3|datasets |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/worker.py", line 81, in loop
3|datasets |     while not has_resources() or not process_next_job():
3|datasets |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/worker.py", line 43, in process_next_job
3|datasets |     refresh_dataset(dataset_name=dataset_name)
3|datasets |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/io/cache.py", line 239, in refresh_dataset
3|datasets |     upsert_dataset(dataset)
3|datasets |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/io/cache.py", line 186, in upsert_dataset
3|datasets |     DbDataset(dataset_name=dataset_name, status="valid").save()
3|datasets |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/mongoengine/document.py", line 430, in save
3|datasets |     raise NotUniqueError(message % err)
3|datasets | mongoengine.errors.NotUniqueError: Tried to save duplicate unique keys (E11000 duplicate key error collection: datasets_preview_cache.datasets index: dataset_name_1 dup key: { dataset_name: "Babelscape/wikineural" }, full error: {'index': 0, 'code': 11000, 'keyPattern': {'dataset_name': 1}, 'keyValue': {'dataset_name': 'Babelscape/wikineural'}, 'errmsg': 'E11000 duplicate key error collection: datasets_preview_cache.datasets index: dataset_name_1 dup key: { dataset_name: "Babelscape/wikineural" }'})
3|datasets | make: *** [Makefile:38: worker] Error 1
```