do less strick check if MailHost is already patched, this avoid useless error in live tests

product/ERP5Type/tests/ERP5TypeTestCase.py

@@ -381,7 +381,7 @@ class ERP5TypeTestCaseMixin(ProcessingNodeTestCase, PortalTestCase):
       """Replace Original Mail Host by Dummy Mail Host in a non-persistent way
       """
       cls = self.portal.MailHost.__class__
-      assert not issubclass(cls, DummyMailHostMixin)
+      if not issubclass(cls, DummyMailHostMixin):
         cls.__bases__ = (DummyMailHostMixin,) + cls.__bases__
         pmc_init_of(cls)