PR for Pandas issue #14872 / fillna() TZ datetime64 rounded
Hi Jeff,

The change adds a "datetime64[ns, UTC]" object to the _DATELIKE_DTYPES set in pandas/types/common.py. 

No such object existed in this set and that is the reason the wrong method was executed on the inputs.

Object is created with "DatetimeTZDtype.__new__"

Thanks,
Rodolfo

 - [X] closes #14872
 - [ X] tests added / passed
 - [ X] passes ``git diff upstream/master | flake8 --diff`` (returns the same number of skips, errors and failures before changes)
 - [ ] whatsnew entry


