BUG: fix to_datetime(dti, utc=True)
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry


ATM `to_datetime(naive_dti, utc=True)` returns naive incorrect, same for naive `DatetimeArray`