fix use of Self

Author: guoci

stdlib/importlib/util.pyi

@@ -1,7 +1,7 @@
 import importlib.machinery
 import sys
 import types
-from _typeshed import ReadableBuffer, Self
+from _typeshed import ReadableBuffer
 from collections.abc import Callable
 from importlib._bootstrap import module_from_spec as module_from_spec, spec_from_loader as spec_from_loader
 from importlib._bootstrap_external import (
@@ -13,7 +13,7 @@ from importlib._bootstrap_external import (
 )
 from importlib.abc import Loader
 from types import TracebackType
-from typing_extensions import ParamSpec, deprecated
+from typing_extensions import ParamSpec, deprecated, Self
 
 _P = ParamSpec("_P")