checkout submodule recursive

.github/workflows/build.yml

@@ -18,7 +18,10 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
+    - name: Checkout repository and submodules
+      uses: actions/checkout@v2
+      with:
+        submodules: recursive
 
     - name: Configure CMake
       # Configure CMake in a 'build' subdirectory. `CMAKE_BUILD_TYPE` is only required if you are using a single-configuration generator such as make.