BUG: DataFrameGroupBy.quantile raises for non-numeric dtypes rather than dropping columns
- [x] closes #27892
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Unlike what is mentioned in #27892, this will raise if there are no columns to aggregate. Both mean and median raise with "No numeric types to aggregate" in such a case, so I was thinking perhaps we should be consistent with them. Any thoughts @WillAyd and @TomAugspurger?


looks like you are including the changes in #34372 here as well @rhshadrach merging master should fix the CI failure. @jreback - the response never updated but Travis passed. Responses to your questions are above. Accidentally deleted PR branch @jreback Friendly ping. Responses to your questions are above. thanks @rhshadrach 