Flaky-test: NamespacesTest.testSubscribeRate (#11394)

Fix #11393 .

Documentation
This is a bug fix, no need to update doc

pulsar-broker/src/test/java/org/apache/pulsar/broker/admin/NamespacesTest.java

@@ -39,6 +39,7 @@
 import java.lang.reflect.Field;
 import java.net.URI;
 import java.net.URL;
+import java.time.Duration;
 import java.util.EnumSet;
 import java.util.HashSet;
 import java.util.List;
@@ -1249,9 +1250,10 @@ public void testSubscribeRate() throws Exception {
         Awaitility.await().untilAsserted(() -> assertFalse(consumer.isConnected()));
 
         // Out of limit period
-        Thread.sleep(6000L);
         pulsarClient.updateServiceUrl(lookupUrl.toString());
-        assertTrue(consumer.isConnected());
+        Awaitility.await()
+                .pollDelay(Duration.ofSeconds(6))
+                .untilAsserted(() -> assertTrue(consumer.isConnected()));
 
         // Disable Subscribe Rate Limiter
         subscribeRate = new SubscribeRate(0, 10);