BUG: DataFrame.resample raised AmbiguousTimeError at a midnight DST transition
- [x] closes #25758
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Going to merge, but let me know if there is any followup I should do.