BUG: Fixes plotting with nullable integers (#32073)
- [x] closes #32073
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Similar to #32410 this tries to fix plotting with nullable integer extension data types by casting them to float before passing on to matplotlib.