Stabilize GitHub Pages deploy job by scoping and preempting workflow concurrency

[Copilot]

The deploy job for the Pages workflow was failing with Deployment cancelled while the deployment remained queued. This change updates workflow-level concurrency so stale deploy attempts no longer block or race the active run.

• Root cause

  • Pages deploy attempts for the same workflow were contending under a shared global concurrency group, leading to queued deployments being canceled.

• Workflow concurrency update

  • Scope concurrency by ref instead of one global pages group.
  • Enable cancellation of older in-progress runs so only the newest run per ref proceeds.

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

• Impact
  • Reduces queued/canceled deploy races and improves determinism of the deploy job for branch updates.