Add missing __init__ for ReferenceType (#12125)

stdlib/weakref.pyi

@@ -41,7 +41,10 @@ _P = ParamSpec("_P")
 ProxyTypes: tuple[type[Any], ...]
 
 class WeakMethod(ref[_CallableT]):
-    def __new__(cls, meth: _CallableT, callback: Callable[[Self], object] | None = None) -> Self: ...
+    # `ref` is implemented in `C` so positional-only arguments are enforced, but not in `WeakMethod`.
+    def __new__(  # pyright: ignore[reportInconsistentConstructor]
+        cls, meth: _CallableT, callback: Callable[[Self], Any] | None = None
+    ) -> Self: ...
     def __call__(self) -> _CallableT | None: ...
     def __eq__(self, other: object) -> bool: ...
     def __ne__(self, other: object) -> bool: ...