[MAINT] fix pytest deprecation

[Remi-Gau]

See

  /home/runner/work/patch-denoising/patch-denoising/examples/conftest.py:7: PytestRemovedIn9Warning: The (path: py.path.local) argument is deprecated, please use (file_path: pathlib.Path)
  see https://docs.pytest.org/en/latest/deprecations.html#py-path-local-arguments-for-hooks-replaced-with-pathlib-path
    def pytest_collect_file(path, parent):

https://github.com/paquiteau/patch-denoising/actions/runs/11210759102/job/31158264458#step:5:56