ERP5Workflow: fix syntax error when handling multiple exceptions

They should be put in a tuple, otherwise, we get the syntax used in:
    try:
      # do something
    except SomeError, e:
      # do something else
where e is the error message

product/ERP5Type/Core/ERP5PersistentMappingFolder.py

@@ -77,7 +77,7 @@ class ERP5PersistentMappingFolder(PortalFolderBase):
     """
     try:
       return self._object_dict[object_id].__of__(self)
-    except KeyError, TypeError: # TypeError if _object_dict is None
+    except (KeyError, TypeError): # TypeError if _object_dict is None
       if default is _marker:
         raise AttributeError(object_id)
       else: