Enable recursive submodule checkout in build workflow

Author: Arlodotexe

.github/workflows/build.yml

@@ -27,6 +27,8 @@ jobs:
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
       - name: Checkout Repository
         uses: actions/checkout@v2
+        with:
+          submodules: recursive
 
       - name: dotnet build
         run: dotnet build /r