BUG: CategoricalDtype.__repr__ with RangeIndex categories
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

The problem was introduced a couple weeks ago, so shouldn't need a whatsnew.
what is the issue where this is are regression? can you add a whatsnew note There is no issue.  The bug isnt in any released version, so doesn't need a whatsnew. kk