Update `TZDateTime` type decorator example to align with python docs

Update `TZDateTime` type decorator example to align with python docs

This change updates the `TZDateTime` type decorator to use the timezone awareness checks described in the Python documentation located here:

https://docs.python.org/3/library/datetime.html#determining-if-an-object-is-aware-or-naive

The specific lines state:

> A [`datetime`](https://docs.python.org/3/library/datetime.html#datetime.datetime) object `d` is aware if both of the following hold:
>
> `d.tzinfo is not None`
>
> `d.tzinfo.utcoffset(d)` does not return `None`
>
> Otherwise, `d` is naive.

Closes: #10719
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/10719
Pull-request-sha: bb30cb3cfe57f326addec21a6cae5f81184c2e74

Change-Id: I1ac51c1ec2820c3f224a79b7af5057fe2b3a55e2