BUG: Categorical setitem, comparison with tuple category
- [x] closes #20439
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

> can you also check getitem?

not sure i follow.  you mean check that `cat[i]` gives a tuple?  pretty sure we already have tests for that > > can you also check getitem?
> 
> not sure i follow. you mean check that `cat[i]` gives a tuple? pretty sure we already have tests for that

ok then.