Incorrect subtyping with bound typevar

From https://github.com/python/typeshed/issues/8372
```
from typing import Callable, TypeVar, Any, Mapping, Optional
T = TypeVar("T", bound=Mapping[str, Any])
def raises(opts: Optional[T]) -> T: pass
def assertRaises(cb: Callable[..., object]) -> None: pass
assertRaises(raises)
```