BUG: setitem with boolean mask and tz-aware DTI
closes #16889 

 - [x] closes #xxxx
 - [x] tests added / passed
 - [x] passes ``git diff upstream/master --name-only -- '*.py' | flake8 --diff`` (On Windows, ``git diff upstream/master -u -- "*.py" | flake8 --diff`` might work as an alternative.)
 - [x] whatsnew entry
