Improve readability of a typing error message to make it clear what is the original type and what is it the type of new variable where overriding failed.
Improve readability of a typing error message to make it clear what is the original type and what is it the type of new variable where overriding failed.

PiperOrigin-RevId: 415231832
Change-Id: I3184964b413ab9ab0eca2cdc78df4ae033f5265b

google/ml_collections,google/ml_collections