BUG: Fix replace for different dtype equal value
Bug noticed when looking at a different issue https://github.com/pandas-dev/pandas/issues/34871#issuecomment-646664842

- [x] closes https://github.com/pandas-dev/pandas/issues/35376
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

can u merge master and will look @dsaxton can you move release note marking as stale :wink: Closing since the other PR looks like a better fix