Type Annotations for df.boxplot
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Thanks for the PR: Could you please sort your imports using isort
```
4.3.21
Check import format using isort
ERROR: /home/runner/work/pandas/pandas/pandas/plotting/_core.py Imports are incorrectly sorted.
``` closing as stale, if you'd like to continue, pls ping.