use a complex model in render_group test

examples/render_groups/main.cpp

@@ -177,8 +177,7 @@ main()
 
 	renDoRenderLoop(rs, 60, doFrameCallbackPre);
 #endif
-	rs->arena = arenaInit();
+	rs->models = assetLoadFromFile(rs->arena, "../data/blender/spaceship.gltf");
-	rs->models = assetLoadFromFile(rs->arena, "../data/blender/icosphere.gltf");
 	assert(rs->models != nullptr);
 	// TODO: need to update model->next somewhere