Bump immutable from 5.1.3 to 5.1.9 in /tgui - #7635

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: eps1lon/actions-label-merge-conflict@1df065ebe6e3310545d4f4c4e862e43bdca146f0. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/