Concurrent creation of parquet files generates errors
See https://huggingface.co/datasets/sil-ai/bloom-vist for example:

<img width="874" alt="Capture d’écran 2023-06-06 à 15 01 11" src="https://github.com/huggingface/datasets-server/assets/1676121/72cb0b13-bb1d-475a-a04c-d9b6f06e3e78">

Half of its configs have no parquet file (thus no number of rows in the select component)

See the details of one of them:

https://datasets-server.huggingface.co/size?dataset=sil-ai/bloom-vist&config=abc

```json
{"error":"412 Client Error: Precondition Failed for url: https://huggingface.co/api/datasets/sil-ai/bloom-vist/commit/refs%2Fconvert%2Fparquet (Request ID: Root=1-647f0082-12624d7b1d357e88202837b3)\n\nA commit has happened since. Please refresh and try again."}
```

It's because of concurrency issues in the creation of parquet files.

Some ideas to solve this:
1. add this error to the retryable errors (by the way: the exception is not properly caught: `UnexpectedError`), then wait for the next backfill cron job to fix them
2. retry immediately, until it's OK

Concurrent creation of parquet files generates errors: See https://huggingface.co/datasets/sil-ai/bloom-vist for example:

<img width="874" alt="Capture d’écran 2023-06-06 à 15 01 11" src="https://github.com/huggingface/datasets-server/assets/1676121/72cb0b13-bb1d-475a-a04c-d9b6f06e3e78">

Half of its configs have no parquet file (thus no number of rows in the select component)

See the details of one of them:

https://datasets-server.huggingface.co/size?dataset=sil-ai/bloom-vist&config=abc

```json
{"error":"412 Client Error: Precondition Failed for url: https://huggingface.co/api/datasets/sil-ai/bloom-vist/commit/refs%2Fconvert%2Fparquet (Request ID: Root=1-647f0082-12624d7b1d357e88202837b3)\n\nA commit has happened since. Please refresh and try again."}
```

It's because of concurrency issues in the creation of parquet files.

Some ideas to solve this:
1. add this error to the retryable errors (by the way: the exception is not properly caught: `UnexpectedError`), then wait for the next backfill cron job to fix them
2. retry immediately, until it's OK
