wlr_scene: Clear damage ring on scale change

If we were trying to change the scale in wlr_scene_output_build_state,
we would be using incorrect damage

types/scene/wlr_scene.c

@@ -1590,6 +1590,10 @@ bool wlr_scene_output_build_state(struct wlr_scene_output *scene_output,
 	}
 
 	if (state->committed & WLR_OUTPUT_STATE_SCALE) {
+		if (render_data.scale != state->scale) {
+			wlr_damage_ring_add_whole(&scene_output->damage_ring);
+		}
+
 		render_data.scale = state->scale;
 	}