Avoid a DeprecationWarning on Python 3.13+

[hroncok]

...
/usr/lib/python3.13/site-packages/jupyter_client/jsonutil.py:31: in <module>
    datetime.strptime("1", "%d")  # noqa
/usr/lib64/python3.13/_strptime.py:573: in _strptime_datetime
    tt, fraction, gmtoff_fraction = _strptime(data_string, format)
/usr/lib64/python3.13/_strptime.py:336: in _strptime
    format_regex = _TimeRE_cache.compile(format)
/usr/lib64/python3.13/_strptime.py:282: in compile
    return re_compile(self.pattern(format), IGNORECASE)
/usr/lib64/python3.13/_strptime.py:270: in pattern
    warnings.warn("""\
E   DeprecationWarning: Parsing dates involving a day of month without a year specified is ambiguious
E   and fails to parse leap day. The default behavior will change in Python 3.15
E   to either always raise an exception or to use a different default year (TBD).
E   To avoid trouble, add a specific year to the input & format.
E   See https://github.com/python/cpython/issues/70647.

Fixes #1020