ci: repin dsx GitHub Actions after org transfer

[lachen-nv]

Summary

• Repin the shared stale-check action from NVIDIA/dsx-github-actions to dsx-ai-factory/dsx-github-actions.
• Update the adjacent documentation URL to the transferred repository.
• Preserve the action path and pinned commit SHA exactly.

Tracking: NvBug 6528755

Validation

• Confirmed the diff is limited to replacing the repository owner/path in .github/workflows/stale-check.yml.
• Confirmed no exact NVIDIA/dsx-github-actions references remain.
• Confirmed both expected dsx-ai-factory/dsx-github-actions references are present.
• Parsed the updated workflow as YAML and ran git diff --check.

Merge timing

Merge this PR only after the repository transfer to dsx-ai-factory/dsx-github-actions is complete.

[copy-pr-bot]

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