Add recursive submodule checkout to API diff workflow

Enable recursive submodule checkout in API diff workflow.

.github/workflows/api-diff.yml

@@ -70,6 +70,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           ref: ${{ steps.pr.outputs.sha }}
+          submodules: recursive
 
       - name: Setup .NET
         uses: actions/setup-dotnet@v4