Test concurrency in parquet and info
It adds a test on the concurrency of job runners on the step `config-parquet-and-info`(which creates `refs/convert/parquet` and uploads parquet files), to detect when the lock is not respected, leading to `CreateCommitError`.

Also:
- group all the code that accesses the Hub inside the lock (create the "branch", send the commit, get the list of files)
- retry "hf_api.list_repo_refs" on connection error (I saw it during the tests)
- adapt the sleep intervals

---

First: tests should fail (https://github.com/huggingface/datasets-server/actions/runs/5335283399/jobs/9668277338)
```
FAILED tests/job_runners/config/test_parquet_and_info.py::test_concurrency - huggingface_hub.utils._errors.HfHubHTTPError: 500 Server Error: Internal Server Error for url: https://hub-ci.huggingface.co/api/datasets/__DUMMY_DATASETS_SERVER_USER__/n_configs-16873575569236/branch/refs%2Fconvert%2Fparquet (Request ID: Root=1-64930878-4a2840cd4fc36b1752b0eac0)
```

Then, after rebasing after merging https://github.com/huggingface/datasets-server/pull/1414 into main, the test should pass (https://github.com/huggingface/datasets-server/actions/runs/5335527787/jobs/9669124731)

Test concurrency in parquet and info: It adds a test on the concurrency of job runners on the step `config-parquet-and-info`(which creates `refs/convert/parquet` and uploads parquet files), to detect when the lock is not respected, leading to `CreateCommitError`.

Also:
- group all the code that accesses the Hub inside the lock (create the "branch", send the commit, get the list of files)
- retry "hf_api.list_repo_refs" on connection error (I saw it during the tests)
- adapt the sleep intervals

---

First: tests should fail (https://github.com/huggingface/datasets-server/actions/runs/5335283399/jobs/9668277338)
```
FAILED tests/job_runners/config/test_parquet_and_info.py::test_concurrency - huggingface_hub.utils._errors.HfHubHTTPError: 500 Server Error: Internal Server Error for url: https://hub-ci.huggingface.co/api/datasets/__DUMMY_DATASETS_SERVER_USER__/n_configs-16873575569236/branch/refs%2Fconvert%2Fparquet (Request ID: Root=1-64930878-4a2840cd4fc36b1752b0eac0)
```

Then, after rebasing after merging https://github.com/huggingface/datasets-server/pull/1414 into main, the test should pass (https://github.com/huggingface/datasets-server/actions/runs/5335527787/jobs/9669124731)
