Add concurrency groups to cancel superseded CI runs

[concaf]

Summary

• Adds concurrency groups with cancel-in-progress: true to all 4 GitHub Actions workflows (build, test, lint, test-e2e)
• When a new push arrives on a PR or main branch, any in-progress workflow run for the same PR/branch is automatically cancelled
• Avoids wasted CI minutes on outdated commits

Test plan

• Push two commits in quick succession to a PR and verify the first run is cancelled
• Verify tag-triggered runs (e.g. v*) are not affected (they get their own concurrency group via github.ref)

[coderabbitai]

Important

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⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Advanced

Run ID: ab665cc9-d951-4be2-a9b8-33893837e8a9

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