Docstring fixes for PR06 errors
This contains some small changes that resolve some of the PR06 errors from running `./scripts/validate_docstrings.py --errors=PR06`
- [x] xref #28724
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
