test: don't use six.iteritems() on msg, the only API is .items()

bt5/erp5_core_test/TestTemplateItem/portal_components/test.erp5.testNotificationTool.py

@@ -51,7 +51,7 @@ def decode_email(file_):
   msg = email.message_from_string(file_.decode())
   # Back up original file
   theMail['__original__'] = file_
-  for key, value in six.iteritems(msg):
+  for key, value in msg.items():
     decoded_value_list = decode_header(value)
     new_value = make_header(decoded_value_list)
     if six.PY2:

bt5/erp5_credential/TestTemplateItem/portal_components/test.erp5.testERP5Credential.py

@@ -175,7 +175,7 @@ class TestERP5Credential(ERP5TypeTestCase):
     msg = email.message_from_string(file_.decode())
     # Back up original file
     theMail['__original__'] = file_
-    for key, value in six.iteritems(msg):
+    for key, value in msg.items():
       decoded_value_list = decode_header(value)
       new_value = make_header(decoded_value_list)
       if six.PY2: