Incompatible signature using `singledispatchmethod` in a subclass

Bug Report

Mypy can't handle singledispatchmethod overloading a method in a subclass

To Reproduce

from functools import singledispatchmethod


class A:
    def foo(self, bar: object) -> object:
        return True


class B(A):
    @singledispatchmethod
    def foo(self, bar: object) -> object:
        return super().foo(bar)

    @foo.register
    def int_impl(self, bar: int) -> int:
        return bar + 2

Expected Behavior

I wasn't expecting any error in this piece of code.

Actual Behavior

test.py:11: error: Signature of "foo" incompatible with supertype "A"  [override]
Found 1 error in 1 file (checked 1 source file)

My Environment

• Mypy version used: 0.990
• Python version used: 3.11

The issue names no repository file or test; start by running the provided Python reproducer against mypy. Trace the incompatible-signature diagnostic around subclass overrides and singledispatchmethod handling, then add regression coverage and verify the example is accepted without errors.