Flaky-test: NamespaceAuthZTest.testPermission

### Search before asking

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

### Example failure

https://github.com/apache/pulsar/actions/runs/8614618958/job/23608820624?pr=22464#step:11:1452

### Exception stacktrace

```
Error: Tests run: 31, Failures: 1, Errors: 0, Skipped: 24, Time elapsed: 14.447 s <<< FAILURE! - in org.apache.pulsar.broker.admin.NamespaceAuthZTest
Error: org.apache.pulsar.broker.admin.NamespaceAuthZTest.testPermission Time elapsed: 0.18 s <<< FAILURE!
org.mockito.exceptions.misusing.UnfinishedStubbingException:

Unfinished stubbing detected here:
-> at org.apache.pulsar.broker.admin.NamespaceAuthZTest.setAuthorizationOperationChecker(NamespaceAuthZTest.java:135)

E.g. thenReturn() may be missing.
Examples of correct stubbing:
when(mock.isOk()).thenReturn(true);
when(mock.isOk()).thenThrow(exception);
doThrow(exception).when(mock).someVoidMethod();
Hints:
1. missing thenReturn()
2. you are trying to stub a final method, which is not supported
3. you are stubbing the behaviour of another mock inside before 'thenReturn' instruction is completed

at org.apache.pulsar.broker.authorization.AuthorizationService.allowNamespaceOperationAsync(AuthorizationService.java:572)
at org.apache.pulsar.broker.admin.NamespaceAuthZTest.setAuthorizationOperationChecker(NamespaceAuthZTest.java:142)
at org.apache.pulsar.broker.admin.NamespaceAuthZTest.testPermission(NamespaceAuthZTest.java:582)
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:840)
```

Mockito isn't thread safe and this could be a problem caused by invalid use of Mockito in multi-threaded code.

### Are you willing to submit a PR?

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