Flaky-test: TransactionEndToEndTest.txnIndividualAckTestNoBatchAndSharedSub

### 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/5872509170/job/15927601818#step:10:1434

### Exception stacktrace

```
Error: Tests run: 41, Failures: 1, Errors: 0, Skipped: 14, Time elapsed: 338.25 s <<< FAILURE! - in org.apache.pulsar.client.impl.TransactionEndToEndTest
Error: org.apache.pulsar.client.impl.TransactionEndToEndTest.txnIndividualAckTestNoBatchAndSharedSub Time elapsed: 20.725 s <<< FAILURE!
java.lang.AssertionError: expected object to not be null
at org.testng.Assert.fail(Assert.java:110)
at org.testng.Assert.assertNotNull(Assert.java:1483)
at org.testng.Assert.assertNotNull(Assert.java:1467)
at org.apache.pulsar.client.impl.TransactionEndToEndTest.txnAckTest(TransactionEndToEndTest.java:533)
at org.apache.pulsar.client.impl.TransactionEndToEndTest.txnIndividualAckTestNoBatchAndSharedSub(TransactionEndToEndTest.java:467)
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 TransactionEndToEndTest.txnIndividualAckTestNoBatchAndSharedSub and inspect TransactionEndToEndTest.java around lines 467 and 533. Compare the failing action with the transaction acknowledgement flow; the test is done when the intermittent null assertion no longer occurs reliably.

Written by the indexing model from the issue text.