Add tests + Dockerfile change - #1

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, docker/build-push-action@0565240e2d4ab88bba5387d719585280857ece09, docker/metadata-action@96383f45573cb7f253c731d3b3ab81c87ef81934, docker/setup-buildx-action@f95db51fddba0c2d1ec667646a06c2ce06100226. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/