DEPR offsets: rename ‘Y’ to ‘YE'
- [x] closes #54275

xref #9586, #52064
Deprecated the alias denoting year end frequency “Y” for offsets in favour of “YE".
@MarcoGorelli, could you please take a look at this PR?  Looks like CI failures are unrelated to my changes (`test_dti_ambiguous_matches_timestamp` in pandas/tests/indexes/datetimes/test_constructors.py failed).