Fix  excel-related docstring errors 
- [x] closes #23494
- [ ] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] passes/runs `python make.py --single pandas.related-doc`

Fix errors which are  reported by `scripts/validate_docstrings.py`:
 
 * pandas.read_excel
 * pandas.io.formats.style.Styler.to_excel
 * Series.to_excel
 * DataFrame.to_excel
