Update typing_extensions imports in third-party stubs (#11245)

stubs/pyserial/serial/serialutil.pyi

@@ -2,8 +2,7 @@ import io
 from _typeshed import ReadableBuffer, WriteableBuffer
 from abc import abstractmethod
 from collections.abc import Callable, Generator
-from typing import Any
-from typing_extensions import Final
+from typing import Any, Final
 
 from serial.rs485 import RS485Settings