Update test-linux.yml

Author: sequoiar

.github/workflows/test-linux.yml

@@ -25,6 +25,8 @@ jobs:
       - uses: actions/checkout@v3
         with:
           persist-credentials: false
+      - name: Checkout submodules
+        run: git submodule update --init --recursive
       - name: Set up Python ${{ env.PYTHON_VERSION }}
         uses: actions/setup-python@v4
         with: