BUG: loc returning wrong elements for non-monotonic DatetimeIndex
- [x] closes #33146
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

That one was tricky. When only one existing key was given or both string parts exist, ``Index.slice_indexer`` is not raising KeyError but selecting a lof of erroneous values
have to look at this in detail Hello @phofl! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:





There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2021-01-03 21:51:10 UTC thanks @phofl very nice. 