ci: request docker socket for image builds

.gitea/workflows/build.yml

@@ -13,6 +13,9 @@ on:
 jobs:
   build:
     runs-on: ubuntu-latest
+    container:
+      volumes:
+        - /var/run/docker.sock:/var/run/docker.sock
     steps:
       - uses: actions/checkout@v7
       - uses: docker/login-action@v3