Audit: bump pulldown-cmark to 0.13.6 - #730

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/upload-artifact@v4, withgraphite/dismiss-all-approvals-js@main. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

No previous SHAs found; behaving as if diff has changed