Stdlib: Deduplicate some multiprocessing type aliases (#9788)

Author: AlexWaygood

stdlib/multiprocessing/dummy/connection.pyi

@@ -1,14 +1,13 @@
+from multiprocessing.connection import _Address
 from queue import Queue
 from types import TracebackType
 from typing import Any
-from typing_extensions import Self, TypeAlias
+from typing_extensions import Self
 
 __all__ = ["Client", "Listener", "Pipe"]
 
 families: list[None]
 
-_Address: TypeAlias = str | tuple[str, int]
-
 class Connection:
     _in: Any
     _out: Any