ci: build & publish the container image too

Signed-off-by: Gergely Nagy <me@gergo.csillger.hu>

.forgejo/workflows/build.yaml

@@ -27,3 +27,24 @@ jobs:
         with:
           logs: true
           package: iocaine
+
+      - name: build the container image
+        uses: actions/nix/build@main
+        with:
+          logs: true
+          package: container-image
+
+      - name: load the container image into docker
+        run: |
+          docker load <result
+
+      - name: login to the container registry
+        uses: https://code.forgejo.org/docker/login-action@v2
+        with:
+          registry: git.madhouse-project.org
+          username: algernon
+          password: ${{ secrets.DOCKER_PASSWORD }}
+
+      - name: publish
+        run:
+          docker push git.madhouse-project.org/algernon/iocaine:latest