Update .gitignore with entries from open PRs and AI tooling - #3495

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, matlab-actions/run-tests@v2, matlab-actions/setup-matlab@v2. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/