Update docker-publish.yml

.github/workflows/docker-publish.yml

@@ -42,7 +42,7 @@ jobs:
     - name: Build Image with pack
       run: |
         pack build ghcr.io/hvg/blog:$TAG \
-        --builder heroku/builder-classic:22 \
+        --builder heroku/buildpacks:20 \
         --descriptor project.toml \
         --workspace /app \
         --env COMPOSER_AUTH=$COMPOSER_AUTH;