[Backport 2.x] Resolve windows opensearch-env.bat having variable delayed expansion issues on OPENSEARCH_HOME assignment introduced in #6956

[opensearch-trigger-bot]

Backport 810b985 from #7080.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      3 org.opensearch.search.SearchWeightedRoutingIT.testStrictWeightedRoutingWithCustomString
      1 org.opensearch.backwards.MixedClusterClientYamlTestSuiteIT.test {p0=pit/10_basic/Delete all}

• URL: https://build.ci.opensearch.org/job/gradle-check/13897/
• CommitID: fa5fadb
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov-commenter]

Codecov Report

Merging #7111 (fa5fadb) into 2.x (b59c826) will increase coverage by 0.03%.
The diff coverage is n/a.

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@@             Coverage Diff              @@
##                2.x    #7111      +/-   ##
============================================
+ Coverage     70.33%   70.37%   +0.03%     
+ Complexity    59575    59550      -25     
============================================
  Files          4824     4824              
  Lines        286321   286321              
  Branches      41624    41624              
============================================
+ Hits         201384   201489     +105     
+ Misses        68100    67980     -120     
- Partials      16837    16852      +15     

see 451 files with indirect coverage changes

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