BUG: GH14233 resample().median() failed if duplicate column names wer…
Simple fix for  median issue.  Should use cython implementation.

 - [X] closes #14233
 - [X] tests added / passed
 - [X] passes ``git diff upstream/master | flake8 --diff``
 - [X] whatsnew entry

lgtm. ping on green. thanks!