fix docker issues & better syntax

.forgejo/workflows/build.yml

@@ -7,13 +7,15 @@ on:
 jobs:
   docker:
     runs-on: docker
-
     steps:
       - name: checkout
         uses: actions/checkout@v4
 
+      - name: set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
       - name: login
-        run: echo "$DOCKER_TOKEN" | docker login -u "$DOCKER_USER" --password-stdin
+        run: echo "${{ secrets.DOCKER_TOKEN }}" | docker login -u "${{ secrets.DOCKER_USER }}" --password-stdin
 
       - name: build
         run: docker build -t $DOCKER_USER/splatnet-backend:latest .