fix(#2249): correct macOS Node, Python and CouchDB steps in dev guide - #2250

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@ee0669bd1cc54295c223e0bb666b733df41de1c5. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/