Enhance error handling and optimize random algorithm for course allocation - #1940

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: garg3133/welcome-new-contributors@v1.1. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/