Enable submodule checkout in Forgejo workflow configuration

.forgejo/workflows/serve.yaml

@@ -8,6 +8,8 @@ jobs:
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
+        with:
+          submodules: "true"
       - name: Initialize virtual environment
         run: /usr/bin/python -m venv .venv
       - name: Install dependencies