Fix a lost wakeup in the unified exec termination test (#47814)

Use `notify_one()` instead of `notify_waiters()` in
`terminating_initial_exec_command_rechecks_initial_response_state` to retain
the release notification if the termination waiter has not registered yet.
This prevents the test from timing out due to a missed notification.

GitOrigin-RevId: d233ffc50e016eb75752fd360a4d846de0063683

codex-rs/core/src/unified_exec/mod_tests.rs

@@ -661,7 +661,8 @@ async fn terminating_initial_exec_command_rechecks_initial_response_state() -> a
             .store(false, std::sync::atomic::Ordering::Release);
     }
 
-    allow_terminate.notify_waiters();
+    // Retain the release even if the sole termination waiter has not registered yet.
+    allow_terminate.notify_one();
     let terminated = tokio::time::timeout(Duration::from_secs(2), terminate_task)
         .await
         .expect("terminate should finish")