Fix shader_prepass example (#15719)

Simple fix for another missed piece in the port to required components

examples/shader/shader_prepass.rs

@@ -212,7 +212,7 @@ impl Material for PrepassOutputMaterial {
 fn toggle_prepass_view(
     mut prepass_view: Local<u32>,
     keycode: Res<ButtonInput<KeyCode>>,
-    material_handle: Query<&Handle<PrepassOutputMaterial>>,
+    material_handle: Query<&MeshMaterial3d<PrepassOutputMaterial>>,
     mut materials: ResMut<Assets<PrepassOutputMaterial>>,
     mut text: Query<&mut Text>,
 ) {