* ADD a new unittest, test_checkDKIM_good_dunno(), to
   test_email_dkim.py, which checks that a received email with two
   ``X-DKIM-Authentication-Results:`` headers (the first one good, the
   second ``dunno``) properly returns False.

 * FIXES #12091. Actually, it doesn't. It just proves that the changes
   in my `fix/9874-automate-email-tests` branch fix #12091. Either way,
   it's fixed, these unittests prove it.