Fix manual split example in process_by_channel_group docs - #4846

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: tj-actions/changed-files@v46.0.1. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/