ci: cancel superseded workflow runs on PR pushes

PR-triggered workflows without a concurrency group keep running (and
holding runner slots) after a force-push or quick follow-up commit
supersedes them. Add the same group/cancel-in-progress block the go
workflow already uses, keyed on head_ref, to the remaining PR workflows.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

.github/workflows/helm_ci.yml

@@ -8,6 +8,10 @@ on:
     branches: [ master ]
     paths: ['k8s/**', '.github/workflows/helm_ci.yml', '.github/scripts/helm_jwt_keys.py']
 
+concurrency:
+  group: ${{ github.head_ref }}/helm_ci
+  cancel-in-progress: true
+
 permissions:
   contents: read