Use TypeAlias where possible for type aliases (#7630)

stdlib/multiprocessing/dummy/connection.pyi

@@ -2,12 +2,13 @@ from _typeshed import Self
 from queue import Queue
 from types import TracebackType
 from typing import Any, Union
+from typing_extensions import TypeAlias
 
 __all__ = ["Client", "Listener", "Pipe"]
 
 families: list[None]
 
-_Address = Union[str, tuple[str, int]]
+_Address: TypeAlias = Union[str, tuple[str, int]]
 
 class Connection:
     _in: Any