[Backport] [2.x] Use BuildParams.isCi() instead of checking env var (#5368)

[reta]

Backport of #5368 to 2.x

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      1 org.opensearch.search.SearchCancellationIT.testCancellationDuringFetchPhaseUsingRequestParameter

• URL: https://build.ci.opensearch.org/job/gradle-check/7318/
• CommitID: 2bfe7b2
  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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.76%. Comparing base (05979b4) to head (2bfe7b2).
⚠️ Report is 2617 commits behind head on 2.x.

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #5372      +/-   ##
============================================
+ Coverage     70.67%   70.76%   +0.08%     
- Complexity    58335    58398      +63     
============================================
  Files          4701     4701              
  Lines        279131   279131              
  Branches      40753    40753              
============================================
+ Hits         197271   197519     +248     
+ Misses        65376    65143     -233     
+ Partials      16484    16469      -15     

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[dreamer-89]

Backport (pull_request_target) workflow is failing with below error. I tried to re-run but it fails instantly with same error. The original PR is already merged into main.
@VachaShah : Do you know why is this failing ?

Error: Error: For security reasons, this action should only run on merged PRs.