need recursive submodule checkout for themes

.forgejo/workflows/image.yaml

@@ -9,6 +9,8 @@ jobs:
     steps:
       - name: Checkout project
         uses: actions/checkout@v4
+        with:
+          submodules: recursive
       - name: Run hugo
         run: docker run --rm -it -v ${{ github.workspace }}:/src docker.io/hugomods/hugo:latest hugo
       - name: Compute Image Metadata