Flaky Test: ClientConfManagerHdfsTest

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)

### Search before asking

- [X] I have searched in the [issues](https://github.com/apache/incubator-uniffle/issues?q=is%3Aissue) and found no similar issues.

### Describe the flaky test

```
Error: Tests run: 1, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 18.644 s <<< FAILURE! - in org.apache.uniffle.test.ClientConfManagerHdfsTest
Error: test Time elapsed: 17.917 s <<< FAILURE!
org.opentest4j.AssertionFailedError: expected: but was:
at org.junit.jupiter.api.AssertionUtils.fail(AssertionUtils.java:55)
at org.junit.jupiter.api.AssertionUtils.failNotEqual(AssertionUtils.java:62)
at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:182)
at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:177)
at org.junit.jupiter.api.Assertions.assertEquals(Assertions.java:1141)
at org.apache.uniffle.test.ClientConfManagerHdfsTest.createAndRunClientConfManagerCases(ClientConfManagerHdfsTest.java:86)
at org.apache.uniffle.test.ClientConfManagerHdfsTest.test(ClientConfManagerHdfsTest.java:46)
```

### Actions URL

https://github.com/apache/incubator-uniffle/actions/runs/4036194515/jobs/6938623599#step:6:3189

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

Start by running ClientConfManagerHdfsTest and inspect the failure at ClientConfManagerHdfsTest.java:86, using the linked GitHub Actions run as the reported reproduction. Trace why the expected value abc becomes null and confirm the test passes reliably across repeated runs.

Written by the indexing model from the issue text.