BUG: DataFrame with mismatched NA value and dtype
- [ ] closes #xxxx
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [x] whatsnew entry

<s>Also fixed the FloatingArray.equals bug on older numpys</s>no longer needed, so reverted