Fix stale-content detection workflow

[aaronpowell]

Summary

The stale-content detection workflow is not reliably identifying outdated entries.

Workflow links

• Workflow definition: https://github.com/github/awesome-copilot/blob/staged/.github/workflows/resource-staleness-report.md
• GitHub run list: https://github.com/github/awesome-copilot/actions/workflows/resource-staleness-report.lock.yml

Scope

• Diagnose current detection and execution failures
• Fix detection criteria and/or workflow execution path
• Validate results against known stale and non-stale samples
• Document the detection behavior and thresholds

Acceptance criteria

• Workflow runs successfully on staged
• Stale content is identified with acceptable precision
• False positives are limited and explainable
• Detection criteria/config are documented

Parent

Part of #2076