BUG: Incorrect addition of Week(weekday=6) to DatetimeIndex
- [ ] closes #22465
- [ ] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Hello @reidy-p! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/tests/arithmetic/test_datetime64.py`](https://github.com/reidy-p/pandas/blob/bca0d9190cc776c4a0d3712910947e44f26331dd/pandas/tests/arithmetic/test_datetime64.py) !

 - There are no PEP8 issues in the file [`pandas/tseries/offsets.py`](https://github.com/reidy-p/pandas/blob/bca0d9190cc776c4a0d3712910947e44f26331dd/pandas/tseries/offsets.py) !

 Great. Since CI is almost done passing, we can just remove it when merging. Thanks for following up on this! Thanks!