[MINOR] fix(test): Fix flaky test SimpleClusterManagerTest#updateExcludeNodesTest

[maobaolong]

What changes were proposed in this pull request?

Fix flaky test SimpleClusterManagerTest#updateExcludeNodesTest

Why are the changes needed?

Error:  Tests run: 10, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 9.317 s <<< FAILURE! - in org.apache.uniffle.coordinator.SimpleClusterManagerTest
Error:  getUnhealthyServerList  Time elapsed: 0.633 s  <<< FAILURE!
org.opentest4j.AssertionFailedError: expected: <[sn4, sn2, sn1]> but was: <[sn2, sn1, sn4, sn3]>
	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.coordinator.SimpleClusterManagerTest.getUnhealthyServerList(SimpleClusterManagerTest.java:219)

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Existing UT

[github-actions]

Test Results

 2 966 files  ±0   2 966 suites  ±0   6h 28m 59s ⏱️ + 1m 34s
 1 100 tests ±0   1 098 ✅ ±0   2 💤 ±0  0 ❌ ±0 
13 774 runs  ±0  13 744 ✅ ±0  30 💤 ±0  0 ❌ ±0 

Results for commit e611f03. ± Comparison against base commit c14bff7.

[cchung100m]

Is it a workaround solution here?

[maobaolong]

Is it a workaround solution here?

@cchung100m Thanks for your review! Actually, no. The purpose of sleep here is specifically to ensure that the file modification time exceeds one second, allowing the subsequent logic to detect a change in the modification time.

[jerqi]

Could use Awaitility.await() instead of sleep? We should wait for a condition instead of a fixed interval.