ci: cancel stale workflow runs

[arturcic]

Summary

• add workflow-level concurrency to all ten head-based validation workflows
• group runs by workflow, event type, and ref
• cancel an older in-progress run when a newer commit starts the same workflow for the same ref
• keep different workflows and event types independent
• leave reusable, release, and downstream publishing workflows unchanged

Validation

• actionlint: zero diagnostics
• verified every non-reusable push/pull-request workflow has the concurrency policy
• git diff --check

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[mergify]

Thank you @arturcic for your contribution!

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud