Use datetime.timezone.utc instead of newer datetime.UTC alias
    
    datetime.UTC alias was added in Python 3.11:
    https://docs.python.org/3/library/datetime.html#datetime.UTC
    
    datetime.timezone.utc was present since Python 3.2.
    
    Since RHEL 9 is using Python 3.9, use more compatible variant.
    
    Fixes: https://pagure.io/freeipa/issue/9454
    
    Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Rafael Guterres Jeffman <rjeffman@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>