Add TypedDict.__{readonly,mutable}_keys__ (#13646)

Author: srittau

stdlib/typing.pyi

@@ -950,6 +950,9 @@ class _TypedDict(Mapping[str, object], metaclass=ABCMeta):
     # so we only add it to the stub on 3.12+
     if sys.version_info >= (3, 12):
         __orig_bases__: ClassVar[tuple[Any, ...]]
+    if sys.version_info >= (3, 13):
+        __readonly_keys__: ClassVar[frozenset[str]]
+        __mutable_keys__: ClassVar[frozenset[str]]
 
     def copy(self) -> typing_extensions.Self: ...
     # Using Never so that only calls using mypy plugin hook that specialize the signature