Flaky Test: GetReaderTest#test

### 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: 4.855 s <<< FAILURE! - in org.apache.uniffle.test.GetReaderTest
Error: test Time elapsed: 3.845 s <<< FAILURE!
org.opentest4j.AssertionFailedError: expected: <2> but was: <0>
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:150)
at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:145)
at org.junit.jupiter.api.Assertions.assertEquals(Assertions.java:527)
at org.apache.uniffle.test.GetReaderTest.test(GetReaderTest.java:150)

```

### Actions URL

https://github.com/apache/incubator-uniffle/actions/runs/4082833774/jobs/7037648782#step:6:4432

### Parent issue

_No response_

### Are you willing to submit PR?

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

Start with GetReaderTest#test and inspect the assertion at GetReaderTest.java:150, then reproduce the failure using the test associated with the linked Actions run. Trace why the test sometimes observes 0 instead of the expected 2; done means the test reliably passes without masking the underlying failure.

Written by the indexing model from the issue text.