BUG: loc raising KeyError for string slices in list-like indexer and DatetimeIndex
- [x] closes #27180
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

I looked into this and added an implementation for list-like indexers containing slices and DatetimeIndexes. If we want to support this we probably have to do something like this.