Mark stub-only types with runtime aliases as @type_check_only in stdlib (#14717)

stdlib/builtins.pyi

@@ -1363,10 +1363,8 @@ class property:
     def __set__(self, instance: Any, value: Any, /) -> None: ...
     def __delete__(self, instance: Any, /) -> None: ...
 
-# This class does not exist at runtime, but stubtest complains if it's marked as
-# @type_check_only because it has an alias that does exist at runtime. See mypy#19568.
-# @type_check_only
 @final
+@type_check_only
 class _NotImplementedType(Any):
     __call__: None