build checkout submodules

.gitea/workflows/build.yaml

@@ -20,6 +20,9 @@ jobs:
 
       - name: Check out repository code
         uses: actions/checkout@v3
+        with:
+          submodules: recursive
+
       - run: echo "The ${{ github.repository }} repository has been cloned to the runner."
 
       - name: Build PDF with `latexmk`