docs(env-vars): raise the SCAN_WORKERS default to 4 - #131

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4.3.0, astral-sh/setup-uv@v6.7.0. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/