Flaky-test: PulsarFunctionsK8STest.testCreateFunctionInK8sWithSecrets

### Search before reporting

- [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/21718811469/job/62651627693?pr=25207#step:12:5662

### Exception stacktrace

```text
Error: Tests run: 2, Failures: 1, Errors: 0, Skipped: 1, Time elapsed: 126.1 s <<< FAILURE! -- in TestSuite
Error: org.apache.pulsar.tests.integration.functions.k8s.PulsarFunctionsK8STest.testCreateFunctionInK8sWithSecrets -- Time elapsed: 0.068 s <<< FAILURE!
org.apache.pulsar.client.admin.PulsarAdminException: Function test-function already exists
at org.apache.pulsar.client.admin.PulsarAdminException.wrap(PulsarAdminException.java:252)
at org.apache.pulsar.client.admin.internal.BaseResource.sync(BaseResource.java:360)
at org.apache.pulsar.client.admin.internal.FunctionsImpl.createFunctionWithUrl(FunctionsImpl.java:199)
at org.apache.pulsar.tests.integration.functions.k8s.PulsarFunctionsK8STest.testCreateFunctionInK8sWithSecrets(PulsarFunctionsK8STest.java:111)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
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:317)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
at java.base/java.lang.Thread.run(Thread.java:1583)
Suppressed: org.apache.pulsar.client.admin.PulsarAdminException: Function test-function already exists
```

### Are you willing to submit a PR?

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

Start with org.apache.pulsar.tests.integration.functions.k8s.PulsarFunctionsK8STest.testCreateFunctionInK8sWithSecrets and the failure at line 111, then inspect the surrounding integration-test setup and the linked CI run. Reproduce the test and determine why test-function already exists; done means the test runs reliably without the existing-function failure.

Written by the indexing model from the issue text.