docker: add checkout action to dockerfile

.github/workflows/build-docker.yaml

@@ -11,6 +11,10 @@ jobs:
     name: Build and push Docker image
     runs-on: ubuntu-latest
     steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+        with:
+          submodules: "true"
 
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v2