Regression in __getitem__ raising for slice DatetimeIndex
- [x] closes #43223
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [x] whatsnew entry

@jbrockmendel Any idea why we used ``maybe_indices_to_slice`` instead of take like in loc?

> Any idea why we used maybe_indices_to_slice instead of take like in loc?

Best guess: if we have e.g. `[0, 2, 4, 6]` that we can change to `slice(0, 8, 2)`, then a) the indexing is no-copy and b) we preserve e.g. DTI.freq and RangeIndex. Hm good point, should we try to convert to slice and only if it fails, e.g. stays an ndarray, call take? > Hm good point, should we try to convert to slice and only if it fails, e.g. stays an ndarray, call take?

i think thats what we're already doing isnt it? I've removed the cast. Added it and we only call take if we can not convert to slice