Inconsistent override check doesn't work with generic functions

Minimal repro:
```
class Base:
    def filter[T](self, iterable: T) -> T:
        ...

class Derived(Base):
    def filter[T](self, iterable: T) -> T:
        ...
```
Expected: No error
Actual:  Class member `Derived.filter` overrides parent class `Base` in an inconsistent manner [bad-override]