Fix Flaky test BacklogQuotaManagerTest.testConsumerBacklogEvictionTimeQuotaWithEmptyLedger (#13724)

diff --git a/pulsar-broker/src/test/java/org/apache/pulsar/broker/service/BacklogQuotaManagerTest.java b/pulsar-broker/src/test/java/org/apache/pulsar/broker/service/BacklogQuotaManagerTest.java
index c61f5d3..2fcc693 100644
--- a/pulsar-broker/src/test/java/org/apache/pulsar/broker/service/BacklogQuotaManagerTest.java
+++ b/pulsar-broker/src/test/java/org/apache/pulsar/broker/service/BacklogQuotaManagerTest.java
@@ -503,6 +503,7 @@
         consumer.receive();
 
         admin.topics().unload(topic);
+        Awaitility.await().until(consumer::isConnected);
         PersistentTopicInternalStats internalStats = admin.topics().getInternalStats(topic);
         assertEquals(internalStats.ledgers.size(), 2);
         assertEquals(internalStats.ledgers.get(1).entries, 0);