ci: implement run concurrency and auto-cancellation in boomtick-pkg ci.yml

[arii]

Description

Adopt concurrency groups on boomtick-pkg's main ci.yml workflow to optimize runner usage and automatically cancel obsolete runs on subsequent branch pushes.

Proposed Changes

1. Edit ci.yml in boomtick-pkg.
2. Add a concurrency configuration block targeting the current branch:

concurrency:
  group: ci-${{ github.ref }}
  cancel-in-progress: true

Verification Checklist

• Verify: Push multiple rapid commits to a test branch → confirm preceding runs are automatically cancelled.

[google-labs-jules]

Jules is on it. When finished, you will see another comment and be able to review a PR.

[google-labs-jules]

Ready for a review! A PR has been created.