[Backport 2.x] Add SplitResponseProcessor to allowlist (#15393)

[dbwiddis]

Backport 2301adf from #15393.

[github-actions]

❌ Gradle check result for 435b817: 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 435b817: 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?

[dbwiddis]

Flaky:

• [AUTOCUT] Gradle Check Flaky Test Report for MinimumClusterManagerNodesIT #14289
• [BUG] org.opensearch.search.basic.SearchWithRandomExceptionsIT.testRandomExceptions {p0={"search.concurrent_segment_search.enabled":"false"}} if flaky #13846

[github-actions]

❌ Gradle check result for 435b817: 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?

[dbwiddis]

Flaky:

• [BUG] org.opensearch.cache.store.disk.EhCacheDiskCacheTests.testComputeIfAbsentConcurrently is flaky #14012

Which is closed:

Closing for now since it does not yet manifests in any merged code

Originally posted by @reta in #14012 (comment)

[github-actions]

✅ Gradle check result for 435b817: SUCCESS

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.56%. Comparing base (4f97fd3) to head (435b817).
Report is 5 commits behind head on 2.x.

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x   #15395      +/-   ##
============================================
+ Coverage     71.52%   71.56%   +0.04%     
- Complexity    63228    63315      +87     
============================================
  Files          5197     5197              
  Lines        296727   296848     +121     
  Branches      43179    43210      +31     
============================================
+ Hits         212221   212434     +213     
+ Misses        66696    66576     -120     
- Partials      17810    17838      +28     

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