Arbitrary attributes are available on `T: Callable`

Those attribute accesses should be errors:

```py
from typing import Callable

def my_decorator[T: Callable](f: T):
    print(f.whatever)
    f.whatever = 1
```
https://play.ty.dev/613cab3e-17be-463e-b5bd-023bf2a72114

(happens for a more specific `Callable` type too)