fix(sync): WebDAV/Upstash sync loses customModels and other mergeWithUpdate fields - #6892

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v2, pplanel/hash-calculator-action@v1.3.1. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/