Fix doc build

[regisss]

What does this PR do?

Recent doc builds failed:

• for main and releases: https://github.com/huggingface/optimum/actions/workflows/build_main_documentation.yml
• for PRs: https://github.com/huggingface/optimum/actions/workflows/build_pr_documentation.yml

It seems Github runners are now configured differently, hence these errors. This PR fixes that.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

Who can review?

[tengomucho]

The optimum-tpu installation fails because torch xla does not support python 3.12 yet, you need to use an earlier version (perhaps the simplest would be to use the ubuntu:22.04 image).

[echarlaix]

Thanks a lot for the fix @regisss !