Docs: adopt the Contributor Covenant 2.1 - #3

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@11d5960a326750d5838078e36cf38b85af677262, github/codeql-action/analyze@c3400c2f38909e0dcf3c3a41f2030a8217be5d3e, github/codeql-action/init@c3400c2f38909e0dcf3c3a41f2030a8217be5d3e. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/