[NFC] Correct the test code in pr65018

The test code in pr65018 is actually incorrect since the optimizier are
free to optimize the whole coroutine body away. This patch corrected
this.

clang/test/CodeGenCoroutines/pr65018.cpp

@@ -17,13 +17,20 @@ struct MyTask {
   // A lazy promise with an await_transform method that supports awaiting
   // integer references using the Awaiter struct above.
   struct promise_type {
-    MyTask get_return_object() { return {}; }
+    MyTask get_return_object() {
+      return MyTask{
+          std::coroutine_handle<promise_type>::from_promise(*this),
+      };
+    }
+
     std::suspend_always initial_suspend() { return {}; }
     std::suspend_always final_suspend() noexcept { return {}; }
     void unhandled_exception();
 
     auto await_transform(const int& x) { return Awaiter{x}; }
   };
+
+  std::coroutine_handle<> h;
 };
 
 // A global array of integers.