Flaky-test: MetadataStoreStatsTest#testBatchMetadataStoreMetrics

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### Example failure

https://github.com/labuladong/pulsar/actions/runs/3376057575/jobs/5603501145#step:10:1208

### Exception stacktrace

Full exception stacktrace

 Error:  Tests run: 7, Failures: 2, Errors: 0, Skipped: 5, Time elapsed: 28.876 s <<< FAILURE! - in org.apache.pulsar.broker.stats.MetadataStoreStatsTest

  Error:  testBatchMetadataStoreMetrics(org.apache.pulsar.broker.stats.MetadataStoreStatsTest)  Time elapsed: 10.577 s  <<< FAILURE!

  java.lang.AssertionError: expected object to not be null

  	at org.testng.Assert.fail(Assert.java:99)

  	at org.testng.Assert.assertNotNull(Assert.java:942)

  	at org.testng.Assert.assertNotNull(Assert.java:926)

  	at org.apache.pulsar.broker.stats.MetadataStoreStatsTest.testBatchMetadataStoreMetrics(MetadataStoreStatsTest.java:185)

  	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

  	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)

  	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

  	at java.base/java.lang.reflect.Method.invoke(Method.java:568)

  	at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:132)

  	at org.testng.internal.InvokeMethodRunnable.runOne(InvokeMethodRunnable.java:45)

  	at org.testng.internal.InvokeMethodRunnable.call(InvokeMethodRunnable.java:73)

  	at org.testng.internal.InvokeMethodRunnable.call(InvokeMethodRunnable.java:11)

  	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)

  	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)

  	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)

  	at java.base/java.lang.Thread.run(Thread.java:833)

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Start with org.apache.pulsar.broker.stats.MetadataStoreStatsTest#testBatchMetadataStoreMetrics and the assertion at MetadataStoreStatsTest.java:185. Run the test repeatedly and investigate why the asserted object is intermittently null. Done means the test passes reliably without the reported assertion failure.

Written by the indexing model from the issue text.