Update concurrency setting for gradle check to exclude cancellation of the post_merge runs

[prudhvigodithi]

Description

Today for a post merge action the running gradle check CI runs are terminated with the concurrency setting.

Here is an example https://github.com/opensearch-project/OpenSearch/actions/runs/14934871450/job/41959850100 where the operation was cancelled by the Github. This can happen when a new PR is merged while for the previous PR post merge run is still running. I assume this is because ${{ github.event.pull_request.number }} shows null for a post merge actions.
But notice this dint actually stop the triggered Jenkins job https://build.ci.opensearch.org/job/gradle-check/57901/. This concurrency setting only terminates at the Github level.

Today for Jenkins this is already handled (https://github.com/opensearch-project/opensearch-build/blob/main/jenkins/gradle/gradle-check.jenkinsfile#L125) to abort the Jenkins jobs for the same PR. So for an open PR upon a new commit when triggered a Jenkins job it will abort the existing running build.

Having this It should be safe to remove the concurrency setting as we dont have to handle the termination at the Github level which is causing the termination of post merge actions. #18283 (comment)

Related Issues

Found when working as part of #17974

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[prudhvigodithi]

Adding @andrross @gaiksaya @getsaurabh02

[andrross]

Does this mean PRs will now get a comment about the cancelled Jenkins job when a new PR revision is pushed?

[prudhvigodithi]

I did some testing and updated to ${{ github.workflow }}-${{ github.event.pull_request.number || github.run_id }}

This still honors cancelling the runs for same PR's

But excludes the post merge events which we can see the runs does not terminate