Make sure we get full file path for filtering in pr-sanity-check (#100978)
The filename get a `.../` path which makes the next diff not work for files that are too nested.
This can seen in https://github.com/pytorch/pytorch/actions/runs/4920598180/jobs/8789553971?pr=100583 for example where most files are ignored.
The detection properly works after this change.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100978
Approved by: https://github.com/seemethere
