Return #type: ignore for Mapping value type variance

Author: ilevkivskyi

stdlib/2/typing.pyi

@@ -233,7 +233,7 @@ class ContextManager(Protocol[_T_co]):
  exc_value: Optional[BaseException],
  traceback: Optional[TracebackType]) -> Optional[bool]: ...
 
-@runtime
+@runtime # type: ignore
 class Mapping(Iterable[_KT], Container[_KT], Sized, Protocol[_KT, _VT_co]):
  # TODO: We wish the key type could also be covariant, but that doesn't work,
  # see discussion in https: //github.com/python/typing/pull/273.

stdlib/3/typing.pyi

@@ -327,7 +327,7 @@ if sys.version_info >= (3, 5):
  exc_value: Optional[BaseException],
  traceback: Optional[TracebackType]) -> Awaitable[Optional[bool]]: ...
 
-@runtime
+@runtime # type: ignore
 class Mapping(_Collection[_KT], Protocol[_KT, _VT_co]):
  # TODO: We wish the key type could also be covariant, but that doesn't work,
  # see discussion in https: //github.com/python/typing/pull/273.