[Backport 3.3] Fix scratch pad when return_history is true

[opensearch-trigger-bot]

Backport 9b11665 from #4310

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.14%. Comparing base (89bac8b) to head (4319e06).

Files with missing lines	Patch %	Lines
...search/ml/engine/tools/ReadFromScratchPadTool.java	75.00%	0 Missing and 1 partial ⚠️
...nsearch/ml/engine/tools/WriteToScratchPadTool.java	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.3    #4316      +/-   ##
============================================
- Coverage     80.14%   80.14%   -0.01%     
+ Complexity    10174    10170       -4     
============================================
  Files           854      854              
  Lines         44231    44219      -12     
  Branches       5117     5113       -4     
============================================
- Hits          35448    35438      -10     
+ Misses         6634     6630       -4     
- Partials       2149     2151       +2     

Flag	Coverage Δ
ml-commons	80.14% <75.00%> (-0.01%)	⬇️

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