BUG: Fix bug in quantile() for resample and groupby with Timedelta
- [x] closes #29485
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Sorry, was waiting for some kind of feedback :) Changed the whatsnew Windows py38_np18 failed to start, Windows py37_np16 failed on `test_binary_arith_ops` (expected). /azp run <samp>
Azure Pipelines successfully started running 1 pipeline(s).<br>

</samp> Same result. @phofl Can you merge master? `test_binary_arith_ops` should now pass and hopefully py38_np18 will start. Done Failure seems unrelated thanks @phofl 