[Backport 2.x] Fix flaky ScalingThreadPoolTests.testScalingThreadPoolConfiguration test (#7539)

[ashking94]

Description

This backports #7539

Related Issues

Resolves #7530

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)

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[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/16036/
• CommitID: 31499f5

[codecov]

Codecov Report

Merging #7689 (31499f5) into 2.x (80aeb76) will decrease coverage by 0.05%.
The diff coverage is 75.53%.

@@             Coverage Diff              @@
##                2.x    #7689      +/-   ##
============================================
- Coverage     70.32%   70.28%   -0.05%     
- Complexity    60112    60121       +9     
============================================
  Files          4892     4892              
  Lines        288859   288899      +40     
  Branches      41972    41978       +6     
============================================
- Hits         203144   203039     -105     
- Misses        68771    68895     +124     
- Partials      16944    16965      +21     

Impacted Files	Coverage Δ
...opensearch/snapshots/mockstore/MockRepository.java	0.00% <0.00%> (ø)
...search/index/shard/RemoteStoreRefreshListener.java	81.88% <82.92%> (+0.40%)	⬆️
...ain/java/org/opensearch/threadpool/ThreadPool.java	82.21% <100.00%> (-1.02%)	⬇️

... and 451 files with indirect coverage changes