BUG: Fix for convert_dtypes with mix of int and string
- [x] closes #32117
- [x] tests added / passed
  - added new cases for `test_convert_dtypes`
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
  - placed in v1.0.2 whatsnew
