Improve the signature of types.MappingProxyType.__eq__

The second parameter is positional-only (I missed this when reviewing #9580)

Author: AlexWaygood

stdlib/types.pyi

@@ -310,7 +310,7 @@ class MappingProxyType(Mapping[_KT, _VT_co], Generic[_KT, _VT_co]):
     def __getitem__(self, __key: _KT) -> _VT_co: ...
     def __iter__(self) -> Iterator[_KT]: ...
     def __len__(self) -> int: ...
-    def __eq__(self, other: object) -> bool: ...
+    def __eq__(self, __value: object) -> bool: ...
     def copy(self) -> dict[_KT, _VT_co]: ...
     def keys(self) -> KeysView[_KT]: ...
     def values(self) -> ValuesView[_VT_co]: ...