Fix FY5253 onOffset/apply bug, simplify
Similar to #18875.

The actual bugfix here is just changing the comparison in `apply` from `other < whatever` to `norm < whatever`.  The remaining edits to `get_year_end` are orthogonal simplification (which I guess could go in a separate PR).

- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
