test: handle failing email signature removal test differently The comment for the test is: # This fails because the sig isn't removed (we currently remove the # sig only if the delimiter is the first line in a section) Originally the test was decorated so it didn't run at all and reported PASSED. The decorator also returned the value 0. This caused a deprecation warning: test/test_mailgw.py::MailgwTestCase::testEmailQuotingRemove3 /usr/lib/python3.12/unittest/case.py:690: DeprecationWarning: It is deprecated to return a value that is not None from a test case [...] Better to handle it using pytest xfail so if we start stripping the signature we get a failure. This does mean the tests get an xfail registered, but I am ok with that. I added "OK" to the reason to indicate it was expected.