Recursively check out submodules in testing workflows

Author: yguclu

.github/workflows/testing.yml

@@ -42,7 +42,7 @@ jobs:
     steps:
       - uses: actions/checkout@v7
         with:
-          submodules: true
+          submodules: 'recursive'
 
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v5