Revert "Only add files with modification outside doc blocks"
Reverts huggingface/transformers#23327.

I apologize, but I read Sylvain's messge too quickly and got it completely wrong.
> for now the tests are launched on a file if we modify it, but I would only launch it if docstrings are modified (e.g. check the modifications are correct) to go faster.

That merged PR did the converse instead: it adds a test file if only docstring (instead of only code) are modified.

I will need to create sth like `diff_is_code_only`.

> Thanks for fixing!
> 
> Apologies for not catching in the review either. In the nightly CI, have we run all of the doctests - or do we expect there to be any untested pieces of code between the merge of #23327 and this PR?

On daily doctest CI, everything is tested :-) - there is no filtration, it just check all files in `utils/documentation_tests.txt`.<|||||>_The documentation is not available anymore as the PR was closed or merged._