test(pubsub): annotate deferred-RunAsync drains (mirror #4327)

Use the same own-line `// RunAsync` marker convention as the bigtable
MutationBatcher deadlock fix (#4327) so the deferred-continuation drains are
immediately recognizable as the same idiom.

Author: klimkina-eris

google/cloud/pubsub/internal/subscription_lease_management_test.cc

@@ -109,13 +109,15 @@ TEST(SubscriptionLeaseManagementTest, NormalLifecycle) {
   // will verify that only the remaining messages have their lease extended.
   uut->AckMessage("ack-0-1");
   fake_cq->SimulateCompletion(true);
-  fake_cq->SimulateCompletion(true);  // drain the deferred OnRefreshTimer
+  // RunAsync, drain the deferred OnRefreshTimer
+  fake_cq->SimulateCompletion(true);
   ASSERT_EQ(1U, fake_cq->size());
 
   // Ack one more message and trigger the new timer.
   uut->NackMessage("ack-0-2");
   fake_cq->SimulateCompletion(true);
-  fake_cq->SimulateCompletion(true);  // drain the deferred OnRefreshTimer
+  // RunAsync, drain the deferred OnRefreshTimer
+  fake_cq->SimulateCompletion(true);
   ASSERT_EQ(1U, fake_cq->size());
 
   shutdown_manager->MarkAsShutdown(__func__, Status{});
@@ -223,7 +225,8 @@ TEST(SubscriptionLeaseManagementTest, UsesDeadlineExtension) {
 
   // Ignore message and then fire the timer. This will extend the deadline.
   fake_cq->SimulateCompletion(true);
-  fake_cq->SimulateCompletion(true);  // drain the deferred OnRefreshTimer
+  // RunAsync, drain the deferred OnRefreshTimer
+  fake_cq->SimulateCompletion(true);
   ASSERT_EQ(1U, fake_cq->size());
 
   shutdown_manager->MarkAsShutdown(__func__, Status{});
@@ -276,7 +279,8 @@ TEST(SubscriptionLeaseManagementTest, ExpiredMessage) {
   // will verify that only the remaining messages have their lease extended.
   uut->AckMessage("ack-0-1");
   fake_cq->SimulateCompletion(true);
-  fake_cq->SimulateCompletion(true);  // drain the deferred OnRefreshTimer
+  // RunAsync, drain the deferred OnRefreshTimer
+  fake_cq->SimulateCompletion(true);
   ASSERT_EQ(1U, fake_cq->size());
 
   shutdown_manager->MarkAsShutdown(__func__, Status{});