[3.9] Fix code-block in zoneinfo (GH-20201)

[miss-islington]

Warning, treated as error:
/tmp/code/Doc/library/zoneinfo.rst:303:Error in "code-block" directive:
1 argument(s) required, 0 supplied.

.. code-block::

    >>> a = ZoneInfo("Europe/Berlin")
    >>> b = pickle.loads(europe_berlin_pkl)
    >>> a is b
    True

(cherry picked from commit 9095f76)

Co-authored-by: Anthony Sottile asottile@umich.edu

[miss-islington]

@asottile: Status check is done, and it's a success ✅ .