Fix warning about multiple enum names when visting the autogenerated OpenAPI

[hmpf]

See also #897

• Warning: encountered multiple names for the same choice set (EventTypesEnum). This may be unwanted even though the generated schema is technically correct. Add an entry to ENUM_NAME_OVERRIDES to fix the naming.

I cannot figure out where drf-spectacular finds something to interpret as EventTypesEnum. There is also TypeEnum with the same contents. Setting ENUM_NAME_OVERRIDES does nothing.