Update box2d-docs-github.yml

Author: VaclavElias

.github/workflows/box2d-docs-github.yml

@@ -22,7 +22,7 @@ jobs:
       uses: actions/checkout@v4
 
     - name: Run Box2D.NET.CommentConverter.csproj
-      run: dotnet run --project tools/Box2D.NET.CommentConverter/Box2D.NET.CommentConverter.csproj --configuration Release
+      run: dotnet run --project tools/Box2D.NET.CommentConverter/Box2D.NET.CommentConverter.csproj --configuration Release --framework net9.0
 
     - name: Install DocFX
       # This installs the latest version of DocFX and may introduce breaking changes