DEPR: deprecate unit parameters ’T’, 't', 'L', and 'l'
- [x] closes #52536
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).

Added upper case ’T’ for minutes in `UnitChoices` list. Now mypy doesn’t raise an error.

Update:
Deprecated unit parameters ’T’, 't', 'L', 'l', and fixed test.
@jbrockmendel, could you please take a look at this pr? along with these i think we need to track down other places where we use/allow these codes.  _attrname_to_abbrevs/_abbrev_to_attrnames and Tick._prefix come to mind.  Doesn't need to be this PR, but hopefully a follow-on Thank you @MarcoGorelli for reviewing this pr. merging then, thanks! Why do this? This is a pain in the ass for people  > Why do this? This is a pain in the ass for people

looks like it comes from [here](https://github.com/pandas-dev/pandas/issues/52536#issuecomment-1581655087)