Add check for required thumbnails in templates - #87

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: Swatinem/rust-cache@779680da715d629ac1d338a641029a2f4372abb5. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/