CI: fix test_matplotlib_scatter_datetime64
- [ ] closes #32440
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

@WillAyd This should be good to go. the web and docs is in a separate PR. Thanks @simonjayhawkins 