Use TypeAlias where possible for type aliases (#7630)

stdlib/multiprocessing/synchronize.pyi

@@ -4,10 +4,11 @@ from contextlib import AbstractContextManager
 from multiprocessing.context import BaseContext
 from types import TracebackType
 from typing import Any, Callable
+from typing_extensions import TypeAlias
 
 __all__ = ["Lock", "RLock", "Semaphore", "BoundedSemaphore", "Condition", "Event"]
 
-_LockLike = Lock | RLock
+_LockLike: TypeAlias = Lock | RLock
 
 class Barrier(threading.Barrier):
     def __init__(