Simplify test code where a dataset is set as gated
[huggingface_hub@0.25.0](https://github.com/huggingface/huggingface_hub/releases/tag/v0.25.0) provides an API to set a repository as gated.

We had included a custom version of `update_repo_settings` because it lacked a `gated` parameter. Now we can switch back to the `huggingface_hub` method

https://github.com/huggingface/dataset-viewer/blob/4859100ef282dcf73257dfb60e6b5a20d5955c68/jobs/cache_maintenance/tests/utils.py#L41
https://github.com/huggingface/dataset-viewer/blob/4859100ef282dcf73257dfb60e6b5a20d5955c68/services/admin/tests/fixtures/hub.py#L24
https://github.com/huggingface/dataset-viewer/blob/4859100ef282dcf73257dfb60e6b5a20d5955c68/services/worker/tests/fixtures/hub.py#L35
Simplify test code where a dataset is set as gated: [huggingface_hub@0.25.0](https://github.com/huggingface/huggingface_hub/releases/tag/v0.25.0) provides an API to set a repository as gated.

We had included a custom version of `update_repo_settings` because it lacked a `gated` parameter. Now we can switch back to the `huggingface_hub` method

https://github.com/huggingface/dataset-viewer/blob/4859100ef282dcf73257dfb60e6b5a20d5955c68/jobs/cache_maintenance/tests/utils.py#L41
https://github.com/huggingface/dataset-viewer/blob/4859100ef282dcf73257dfb60e6b5a20d5955c68/services/admin/tests/fixtures/hub.py#L24
https://github.com/huggingface/dataset-viewer/blob/4859100ef282dcf73257dfb60e6b5a20d5955c68/services/worker/tests/fixtures/hub.py#L35