fix(ci): use docker-ready runner label in Forgejo workflow

- Change runs-on from self-hosted to docker-ready
- Add DOCKER_HOST and DOCKER_BUILDKIT env vars
- Align with other repo workflows

.forgejo/workflows/build.yaml

@@ -12,7 +12,10 @@ concurrency:
 
 jobs:
   build:
-    runs-on: self-hosted
+    runs-on: docker-ready
+    env:
+      DOCKER_HOST: tcp://127.0.0.1:2375
+      DOCKER_BUILDKIT: "1"
     steps:
       - name: Checkout
         uses: actions/checkout@v4