Bump browserslist from 4.20.3 to 4.28.8 in /rescript-relay-documentation - #663

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, actions/setup-node@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Input 'dune-cache' has been deprecated with message: This input will be removed in v4. The "cache" input takes precedence: "cache: false" disables Dune caching. Manage Dune caching separately after removal.