BUG: Validate drop_duplicates ignore_index argument for bool
- [x] closes #38274
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Saw this on the tracker. I think we should validate this, some inputs could lead to weird results.
The last drop duplicates entry in whatsnew was also under reshaping, so put it there