docs: update app workshops for Issues and Pull requests and sync first steps with upstream - #194

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/

Summary report available at: https://github.com/github-samples/copilot-workshops/actions/runs/37351373070#summary-111902764781