BUG: DataFrame[object] + Series[dt64], test parametrization
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

In the course of parametrizing tests, found a failing case.  The edit in ops.dispatch fixes it.