Update tests/server-common/src/test/java/org/a2aproject/sdk/server/apps/common/AbstractA2AServerTest.java

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: jmesnil

tests/server-common/src/test/java/org/a2aproject/sdk/server/apps/common/AbstractA2AServerTest.java

@@ -806,8 +806,8 @@ public void testSubscribeExistingTaskSuccess() throws Exception {
 
             // Wait for EventConsumer polling loop to start (transport-level subscription
             // does not guarantee the consumer is ready to receive events)
-            assertTrue(waitForChildQueueCountToBe(MINIMAL_TASK.id(), childCountBefore + 1, 15000),
-                    "subscribeToTask child queue should be created");
+            assertTrue(awaitChildQueueCountStable(MINIMAL_TASK.id(), childCountBefore + 1, 15000),
+                    "subscribeToTask child queue should be created and stable");
 
             // Enqueue events on the server
             List<Event> events = List.of(