Fix clear transaction buffer snapshot flaky test (apache#14922)

### Motivation
```
java.lang.AssertionError: 
Expected :true
Actual   :false
<Click to see difference>
	at org.testng.Assert.fail(Assert.java:99)
	at org.testng.Assert.failNotEquals(Assert.java:1037)
	at org.testng.Assert.assertTrue(Assert.java:45)
	at org.testng.Assert.assertTrue(Assert.java:55)
	at org.apache.pulsar.broker.transaction.TopicTransactionBufferRecoverTest.checkSnapshotCount(TopicTransactionBufferRecoverTest.java:452)
	at org.apache.pulsar.broker.transaction.TopicTransactionBufferRecoverTest.clearTransactionBufferSnapshotTest(TopicTransactionBufferRecoverTest.java:427)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:132)
// ...
```

Currently, the clear transaction buffer snapshot is flaky, because we used `@Cleanup` annotation, the `@Cleanup` annotation will put the close producer method to the bottom of the test method, then the producer will close after deleting the topic. 

When we delete the topic, all relevant producers will receive a `CLOSE_PRODUCER` command, then the producer client will try to reconnect to the broker, so it will send the `PRODUCER` command again, then the transaction buffer snapshot will take a new snapshot, so the test will fail.

### Modifications

Make the producer close before the topic deleting.

pulsar-broker/src/test/java/org/apache/pulsar/broker/transaction/TopicTransactionBufferRecoverTest.java

@@ -391,7 +391,6 @@ private void testTopicTransactionBufferDeleteAbort() throws Exception {
     public void clearTransactionBufferSnapshotTest() throws Exception {
         String topic = NAMESPACE1 + "/tb-snapshot-delete-" + RandomUtils.nextInt();
 
-        @Cleanup
         Producer<byte[]> producer = pulsarClient
                 .newProducer()
                 .topic(topic)
@@ -404,6 +403,7 @@ public void clearTransactionBufferSnapshotTest() throws Exception {
         producer.newMessage(txn).value("test".getBytes()).sendAsync();
         producer.newMessage(txn).value("test".getBytes()).sendAsync();
         txn.commit().get();
+        producer.close();
 
         // take snapshot
         PersistentTopic originalTopic = (PersistentTopic) getPulsarServiceList().get(0)