DOC: object_dtype_tzaware_strings.atype(dt64) raises
- [x] closes #50140 (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [x] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Thanks @jbrockmendel  To be explicit about the implications of doing this as a breaking change: this breaks pandas<->pyarrow roundtrips, and so eg also pandas<->parquet roundtripping (admittedly, in a somewhat corner case of using a DatetimeIndex for the column labels)

So users doing pd.read_parquet(..) with a file they wrote earlier will now get an error (with released pyarrow) that they can't easily solve themselves.