Positional-or-kw arg considered incompatible with positional-only argument

Bug Report

from typing_extensions import Protocol


class Func(Protocol):
    def __call__(self, __a: int, **kwargs: str) -> None:
        #              ^^^ positional-only arg
        ...
    # Same error when using PEP 570 positional-only syntax:
    # def __call__(self, a: int, /, **kwargs: str) -> None:


def myfunc(a: int, **kwargs: str) -> None:
    pass


f: Func = myfunc

Expected Behavior

In my view this should be allowed. Anyone calling f() promises to pass the 1st argument as positional. And myfunc accepts the 1st argument as positional or kwarg, so it should be considered compatible.

Actual Behavior

Mypy output:

positional_only.py:12: error: Incompatible types in assignment (expression has type "Callable[[int, KwArg(str)], Any]", variable has type "Func")
positional_only.py:12: note: "Func.__call__" has type "Callable[[int, KwArg(str)], Any]"

Your Environment

• Mypy version used: 0.942
• Mypy command-line flags: (none)
• Mypy configuration options from mypy.ini (and other config files): (none)
• Python version used: 3.10.2
• Operating system and version: macOS

Run the provided Python example with mypy and confirm the incompatible assignment diagnostic for the Protocol callable. Trace the callable compatibility handling for positional-only and positional-or-keyword parameters, then add a regression test showing that this assignment is accepted while incompatible calls remain rejected.