[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

Merging #5372 (2bfe7b2) into 2.x (05979b4) will increase coverage by 0.08%.
The diff coverage is n/a.

@@             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     

Impacted Files	Coverage Δ
...search/indices/recovery/RecoveryTargetHandler.java	0.00% <0.00%> (-100.00%)	⬇️
...n/indices/forcemerge/ForceMergeRequestBuilder.java	0.00% <0.00%> (-75.00%)	⬇️
.../indices/forcemerge/TransportForceMergeAction.java	25.00% <0.00%> (-75.00%)	⬇️
...regations/metrics/AbstractHyperLogLogPlusPlus.java	51.72% <0.00%> (-44.83%)	⬇️
...cluster/coordination/PublishClusterStateStats.java	33.33% <0.00%> (-37.51%)	⬇️
...nsearch/index/shard/IndexShardClosedException.java	66.66% <0.00%> (-33.34%)	⬇️
...on/admin/indices/forcemerge/ForceMergeRequest.java	52.77% <0.00%> (-33.34%)	⬇️
...rc/main/java/org/opensearch/ingest/IngestInfo.java	51.72% <0.00%> (-27.59%)	⬇️
...opensearch/snapshots/SnapshotRestoreException.java	25.00% <0.00%> (-25.00%)	⬇️
...a/org/opensearch/transport/netty4/Netty4Utils.java	42.42% <0.00%> (-21.22%)	⬇️
... and 471 more

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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.