Update actions to include submodule checkout

.github/workflows/ccpp.yml

@@ -9,6 +9,8 @@ jobs:
     
     steps:
     - uses: actions/checkout@v1
+    - name: Checkout submodules
+      uses: textbook/git-checkout-submodule-action@2.0.0
     - name: make
       run: cd src && make -d V=1
     - name: make check