ci: drop deprecated soldeer-generate-cmd input - #249

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5, nix-community/cache-nix-action@135667ec418502fa5a3598af6fb9eb733888ce6a. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/