Flaky-test: MetadataStoreStatsTest.testMetadataStoreStats

### Search before asking

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

### Example failure

https://github.com/michaeljmarshall/pulsar/actions/runs/4117926823/jobs/7110068497#step:11:1262

### Exception stacktrace

```
Error: Tests run: 7, Failures: 1, Errors: 0, Skipped: 5, Time elapsed: 18.502 s <<< FAILURE! - in org.apache.pulsar.broker.stats.MetadataStoreStatsTest
Error: testMetadataStoreStats(org.apache.pulsar.broker.stats.MetadataStoreStatsTest) Time elapsed: 0.735 s <<< FAILURE!
java.lang.AssertionError:
Assertion failed with metrics:

(omitted metrics)

expected object to not be null
at org.testng.Assert.fail(Assert.java:110)
at org.testng.Assert.assertNotNull(Assert.java:1319)
at org.apache.pulsar.broker.stats.MetadataStoreStatsTest.testMetadataStoreStats(MetadataStoreStatsTest.java:113)
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.invokers.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:139)
at org.testng.internal.invokers.InvokeMethodRunnable.runOne(InvokeMethodRunnable.java:47)
at org.testng.internal.invokers.InvokeMethodRunnable.call(InvokeMethodRunnable.java:76)
at org.testng.internal.invokers.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 by running org.apache.pulsar.broker.stats.MetadataStoreStatsTest.testMetadataStoreStats and inspect the failure at MetadataStoreStatsTest.java:113. Compare repeated runs with the linked CI failure and determine why the expected metrics object is sometimes null. Done means the test reliably passes without weakening its metrics assertion.

Written by the indexing model from the issue text.