dependency: (deps): bump idna from 3.18 to 3.19 in /backend - #796

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: dependabot/fetch-metadata@v1. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/