BUG: get_indexer_non_unique not excluding boolean like get_indexer
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

There's a check in get_indexer that is missing from get_indexer_non_unique, which this adds.  This is going to make some de-duplication easier.

Hard to find a user-facing example bc indexing with all-bool indexer we treat it as a mask and not a list of labels.  The closest I got to a user-facing example was in Series.drop, but that ran in to #38051.