BUG: Fix passing of numeric_only argument for categorical reduce
See https://github.com/pandas-dev/pandas/issues/25303 and https://github.com/pandas-dev/pandas/issues/25299

- [x] closes https://github.com/pandas-dev/pandas/issues/25299
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
