Fix various __all__-related typos and omissions (#7378)

stdlib/asyncio/windows_utils.pyi

@@ -10,6 +10,9 @@ if sys.platform == "win32":
         __all__ = ("pipe", "Popen", "PIPE", "PipeHandle")
     else:
         __all__ = ["socketpair", "pipe", "Popen", "PIPE", "PipeHandle"]
+        import socket
+
+        socketpair = socket.socketpair
 
     class _WarnFunction(Protocol):
         def __call__(