[Backport 2.x] Improve tests.config property thread safety

[opensearch-trigger-bot]

Backport cc2b704 from #5645.

[codecov-commenter]

Codecov Report

Merging #5654 (c9966e9) into 2.x (5ff33de) will increase coverage by 0.08%.
The diff coverage is 33.33%.

@@             Coverage Diff              @@
##                2.x    #5654      +/-   ##
============================================
+ Coverage     70.61%   70.69%   +0.08%     
- Complexity    58605    58692      +87     
============================================
  Files          4740     4740              
  Lines        280513   280514       +1     
  Branches      40881    40881              
============================================
+ Hits         198075   198318     +243     
+ Misses        65914    65724     -190     
+ Partials      16524    16472      -52     

Impacted Files	Coverage Δ
.../org/opensearch/bootstrap/BootstrapForTesting.java	77.06% <33.33%> (+0.21%)	⬆️
...n/indices/forcemerge/ForceMergeRequestBuilder.java	0.00% <0.00%> (-75.00%)	⬇️
.../indices/forcemerge/TransportForceMergeAction.java	25.00% <0.00%> (-75.00%)	⬇️
...a/org/opensearch/tasks/TaskCancelledException.java	50.00% <0.00%> (-50.00%)	⬇️
.../opensearch/client/indices/CloseIndexResponse.java	42.50% <0.00%> (-48.75%)	⬇️
...cluster/coordination/PendingClusterStateStats.java	20.00% <0.00%> (-48.00%)	⬇️
...java/org/opensearch/threadpool/ThreadPoolInfo.java	56.25% <0.00%> (-37.50%)	⬇️
...r/src/main/java/org/opensearch/http/HttpUtils.java	33.33% <0.00%> (-33.34%)	⬇️
...on/admin/indices/forcemerge/ForceMergeRequest.java	52.77% <0.00%> (-33.34%)	⬇️
...arch/search/aggregations/pipeline/SimpleModel.java	38.46% <0.00%> (-30.77%)	⬇️
... and 481 more

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[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/8580/
• CommitID: c9966e9