Fix double dots in data files
_The documentation is not available anymore as the PR was closed or merged._ The CI fails are unrelated to this PR (apparently something related to `seqeval` on windows) - merging :)
As mentioned in https://github.com/huggingface/transformers/pull/17715 `data_files` can't find a file if the path contains double dots `/../`. This has been introduced in https://github.com/huggingface/datasets/pull/4412, by trying to ignore hidden files and directories (i.e. if they start with a dot)

I fixed this and added a test

cc @sgugger @ydshieh 