arguments list is empty if define __call__ as attribute of class

Bug Report

arguments list is empty if define __call__ as attribute of class

To Reproduce

import typing


class Bug:
    __slots__ = ("__call__",)
    __call__: typing.Callable[[int], bytes]

    @staticmethod
    def test(_x: int) -> bytes:
        return b""

    def __init__(self) -> None:
        self.__call__ = Bug.test


def bug() -> typing.Callable[[int], bytes]:
    return Bug()


if __name__ == "__main__":
    bug()

Expected Behavior

pass

Actual Behavior

test.py:17: error: Incompatible return value type (got "Bug", expected "Callable[[int], bytes]")  [return-value]
test.py:17: note: "Bug.__call__" has type "Callable[[], bytes]"
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 1.8.0
• Mypy command-line flags: --strict test.py
• Mypy configuration options from mypy.ini (and other config files): default mypy, no config
• Python version used: CPython 3.11.6

No repository file or test is named. Start by saving the supplied example as test.py and running mypy --strict test.py; then trace how mypy types a class instance whose call is declared as a slot attribute. Done means the example passes without the incompatible return-value error.