Fix Learning Hub update workflow

[aaronpowell]

Summary

The Learning Hub update workflow is currently broken and not keeping content in sync.

Workflow links

• Workflow definition: https://github.com/github/awesome-copilot/blob/staged/.github/workflows/learning-hub-updater.md
• GitHub run list: https://github.com/github/awesome-copilot/actions/workflows/learning-hub-updater.lock.yml

Scope

• Diagnose root cause in the current workflow
• Repair update logic and supporting workflow configuration
• Validate expected content update behavior end-to-end
• Document any required environment/config updates

Acceptance criteria

• Workflow completes successfully on staged
• Learning Hub updates are generated/applied as expected
• Failures provide actionable errors (no silent failures)
• Documentation is updated for any changed setup/behavior

Parent

Part of #2076