Add Nexus Shell as a macOS Fleet-maintained app - #50822

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@1bd1e32a3bdc45362d1e726936510720a7c30a57, actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9, actions/setup-node@5e21ff4d9bc1a8cf6de233a3057d20ec6b3fb69d, actions/upload-artifact@6f51ac03b9356f520e9adb1b1b7802705f340c2b. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/