Add types.UnionType.__parameters__ (#13628)

annotate the `types.UnionType.__parameters__` property

Author: jorenham

stdlib/types.pyi

@@ -687,6 +687,8 @@ if sys.version_info >= (3, 10):
     class UnionType:
         @property
         def __args__(self) -> tuple[Any, ...]: ...
+        @property
+        def __parameters__(self) -> tuple[Any, ...]: ...
         def __or__(self, value: Any, /) -> UnionType: ...
         def __ror__(self, value: Any, /) -> UnionType: ...
         def __eq__(self, value: object, /) -> bool: ...