API/BUG: treat different UTC tzinfos as equal
- [x] closes #23959
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

> can you add a whatsnew note (bug fix ok).

updated

> any perf diffs here?

tz_compare checks will be slightly slower, but we'll avoid casting to object in a few cases.  not much