Upgrade Rails to ~> 8.1, Grape to ~> 3.3, update all dependencies - #114

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v3, coactions/setup-xvfb@v1. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/