FIX: allow sorting by tuple of column names
- [ ] closes #36268
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Turns out that ``by=(some, tuple)`` is reserved to sorting by multilevel columns.
Thus, these changes are not to be implemented.