gtk: allocate Gtk memory with 'atomic-interior - #375

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v3.3.0, actions/upload-artifact@v4, Bogdanp/setup-racket@v1.9.1. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/