BUG: Do not allow boolean values for indexing with .loc without a boolean index.
- [x] closes #20432
- [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

Please add whatsnew  > Please add whatsnew

Added. CI failure seems related > CI failure seems related

Yes, indeed. I could fix most of the failing tests with specifying the dtypes. But for some reason specifying dtype="boolean" does not remove the warning. This is a separate issue though. > > CI failure seems related
> 
> Yes, indeed. I could fix most of the failing tests with specifying the dtypes. But for some reason specifying dtype="boolean" does not remove the warning. This is a separate issue though.

I must have been tired. dtype="boolean" was not passed to the df or series, but to the index. Fixed and expect CI to be green. Small comments, otherwise lgtm, pls merge master too Hello @DriesSchaumont! 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 2021-04-06 15:29:28 UTC lgtm cc @jreback @jbrockmendel  @DriesSchaumont did you post the updated asv's?  https://github.com/pandas-dev/pandas/pull/40726#discussion_r606390899

Here  @phofl pls merge! thanks @DriesSchaumont 