🧲 Use our own `require_bitsandbytes`

[qgallouedec]

What does this PR do?

To avoid this warning in our tests:

../transformers/src/transformers/testing_utils.py:1163
  /fsx/qgallouedec/transformers/src/transformers/testing_utils.py:1163: PytestUnknownMarkWarning: Unknown pytest.mark.bitsandbytes - is this a typo?  You can register custom marks to avoid this warning - for details, see https://docs.pytest.org/en/stable/how-to/mark.html
    return pytest.mark.bitsandbytes(test_case)

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

Before submitting

• [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• [ ] Did you read the contributor guideline, Pull Request section?
• [ ] Was this discussed/approved via a GitHub issue? Please add a link to it if that's the case.
• [ ] Did you make sure to update the documentation with your changes? Here are the documentation guidelines.
• [ ] Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag members/contributors who may be interested in your PR.

[HuggingFaceDocBuilderDev]

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[qgallouedec]

Failing test not related (fixed in #2373)