fix(cli): refuse a non-URL install-from-source source up front - #3166

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache/restore@0057852bfaa89a56745cba8c7296529d2fc39830, pnpm/action-setup@41ff72655975bd51cab0327fa583b6e92b6d3061. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/