Fix stdlib stubtest for latest Python patch releases (#13464)

stdlib/posix.pyi

@@ -379,6 +379,7 @@ if sys.platform != "win32":
                 CLONE_SYSVSEM as CLONE_SYSVSEM,
                 CLONE_THREAD as CLONE_THREAD,
                 CLONE_VM as CLONE_VM,
+                PIDFD_NONBLOCK as PIDFD_NONBLOCK,
                 setns as setns,
                 unshare as unshare,
             )