mypy

2c6e43e1 - Stubtest: check that the stub is abstract if the runtime is, even when the stub is an overloaded method (#14955)

Stubtest: check that the stub is abstract if the runtime is, even when the stub is an overloaded method (#14955) #13323 means that stubtest will currently emit an error if the runtime is decorated with `@abstractmethod` but the stub is not, but _only_ if the stub is not an overloaded function, as overloaded functions have a different internal representation in mypy. This PR fixes that discrepancy.