BUG: Ensure read_spss accepts pathlib Paths (GH33666)
- [x] closes #33666
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Wrapped the `path` passed into `pandas.io.spss.read_spss` in a `pandas.io.common.stringify_path` call prior to passing it to `pyreadstat.read_sav`. This fixes #33666. I've also included tests validating `pd.read_spss` accepts strings and `pathlib.Path`s.