TST: DataFrame.replace: TypeError: Cannot compare types 'ndarray(dtype=int64)' and 'unicode'
- [x] closes #16784
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Thanks @jbrockmendel for fixing my related issue
Test failure looks unrelated? thanks @phofl 