[gunicorn] Add BaseSocket.sock (#14946)

stubs/gunicorn/gunicorn/sock.pyi

@@ -9,6 +9,8 @@ from gunicorn.glogging import Logger as GLogger
 from .config import Config
 
 class BaseSocket:
+    sock: socket.socket
+
     def __init__(self, address: str, conf: Config, log: GLogger, fd: SupportsIndex | None = None) -> None: ...
     def __getattr__(self, name: str) -> Any: ...
     def set_options(self, sock: socket.socket, bound: bool = False) -> socket.socket: ...