ui_dump_test: No need to track Activities.

This also avoids KeyError exceptions when Activities have already been processed
in the meantime.

product/ERP5Type/tests/ui_dump_test.py

@@ -121,6 +121,7 @@ class ui_dump_test(object):
   _module_tracking_blacklist = {
     'portal_simulation',
     'portal_solver_processes',
+    'portal_activities',
   }
 
   def trackObject(self, path, ob):