(🐞) 1.2 regression invalid error and bad message with Concatenate return value

[KotlinIsland]

from typing import Callable, Concatenate, Generic, ParamSpec, TypeVar

R = TypeVar("R")
P = ParamSpec("P")

def f() -> Callable[[Callable[Concatenate[str, P], R]], Callable[P, R]]:
    def decorator(fn: Callable[Concatenate[str, P], R], /) -> Callable[P, R]:
        ...

    return decorator

playground

Incompatible return value type (got "Callable[[Callable[[str, **P], R]], Callable[P, R]]", expected "Callable[[Callable[[str, **P], R]], Callable[P, R]]")

[A5rocks]

Yet another thing fixed by #15272, lol

I don't really get how that PR fixes so many issues honestly