Fix flaky TransportMultiSearchActionTests.testCancellation

[kkewwei]

Description

When I put the PR #18069 with the newest main branch, the ci throws the exception, as shown in this link: TransportMultiSearchActionTests.testCancellation:
https://build.ci.opensearch.org/job/gradle-check/57253/

Here are two scenarios regarding this issue:

1. If the unit test executes too quickly, the async search might not get a chance to execute, so the unit test seems doesn't work.
2. On the other hand, if the unit test does not execute quickly, it may trigger the exception, which is the case I encountered.
   https://github.com/opensearch-project/OpenSearch/blob/main/server/src/test/java/org/opensearch/action/search/TransportMultiSearchActionTests.java#L402

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[kkewwei]

@msfroh Please have a look in your spare time, I saw you have also fixed the flaky TransportMultiSearchActionTests.testCancellation in #17193

[github-actions]

❌ Gradle check result for 7084c40: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

✅ Gradle check result for 7084c40: SUCCESS

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.41%. Comparing base (a6724d3) to head (3839317).
Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #18099      +/-   ##
============================================
- Coverage     72.53%   72.41%   -0.13%     
+ Complexity    67207    67121      -86     
============================================
  Files          5476     5476              
  Lines        310436   310436              
  Branches      45121    45121              
============================================
- Hits         225179   224803     -376     
- Misses        66894    67319     +425     
+ Partials      18363    18314      -49     

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[github-actions]

❌ Gradle check result for 589df35: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for 589df35: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[kotwanikunal]

@kkewwei Mind rebasing your PR? We have muted a few flaky more tests with #18142

[andrross]

@kotwanikunal I just pushed a rebase commit

[github-actions]

❕ Gradle check result for 3839317: UNSTABLE

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.