Stack CI: clone Andreas' solution with shallow submodules

It uses Runtime.java from the lab2-testsuite

Author: andreasabel

Diff for: .github/workflows/stack.yml

@@ -34,6 +34,7 @@ jobs:
       uses: actions/checkout@v4
       with:
         repository: teach-plt/lab-solutions-andreas
+        submodules: true
         path: lab-solutions-andreas
         ssh-key: ${{ secrets.PRIVATE_READ_ACCESS_TOKEN }}