Regression in classmethod override #5259

[case testClassMethodOverride]
from typing import Callable, Any

def deco(f: Callable[..., Any]) -> Callable[..., Any]: ...

class B:
    @classmethod
    def meth(cls, x: int) -> int: ...

class C(B):
    @classmethod
    @deco
    def meth(cls, x: int) -> int: ...
[builtins fixtures/classmethod.pyi]
[out]