manifest: Weekly sdk-nrf / sdk-connectedhomeip sync test - #6

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@d4323d4df104b026a6aa633fdb11d772146be0bf, actions/upload-artifact@c7d193f32edcb7bfad88892161225aeda64e9392. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/