Add concurrency control to schema PR preview workflow

[Copilot]

Description

Adds concurrency configuration to the schema PR preview workflow to prevent stale runs from overwriting newer previews in S3/CloudFront when multiple pushes land in quick succession on the same PR.

concurrency:
  group: schema-pr-preview-${{ github.event.number }}
  cancel-in-progress: true

Reference

1. [FEATURE] Docs preview for schema changes #473

Testing

No functional logic changed — CI behavior change only. The concurrency group is keyed per PR number, so runs across different PRs are unaffected.

Checklist

1. Add relevant examples.
2. Add relevant counterexamples.
3. Update any counterexamples that became obsolete. For example, if a counterexample uses property A but is not intended to test property A's validity, and you made a schema change that invalidates property A in that counterexample, fix the counterexample to align it with your schema change.
4. Update in-schema documentation using plain English written in complete sentences, if an update is required.
5. Update Docusaurus documentation, if an update is required.
6. Review change with Overture technical writer to ensure any advanced documentation needs will be taken care of, unless the change is trivial and would not affect the documentation.

Documentation website

Docs preview for this PR.

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[John McCall (lowlydba)]

Already did it manually via 8fe999b on the parent PR's branch

[github-actions]

🗺️ Schema reference docs preview is live!

🌍 Preview	https://staging.overturemaps.org/schema/pr/482/schema/index.html
🕐 Updated	Mar 23, 2026 16:05 UTC
📝 Commit	e006141
🔧 env SCHEMA_PREVIEW	true

Note

♻️ This preview updates automatically with each push to this PR.