Fix scheduled workflow token handling

[SamuelMcAravey]

Fix the scheduled workflow failures in ChatKit dotnet.

• Route create-pull-request through WORKBENCH_GITHUB_TOKEN fallback.
• Move the ChatKit JS upstream clone out of the repository working tree so the check step no longer sees a dirty tree.

Validation: git diff --check.

[github-actions]

Test Docs Summary

• Total tests: 89
• Compliant: 89 (100.0%)
• Missing required: 0
• Invalid format: 0

Artifacts: testdocs (docs/testing/generated)