Fix prepass batch (#13943)

# Objective

- After #11804 , The queue_prepass_material_meshes function is now
executed in parallel with other queue_* systems. This optimization
introduced a potential issue where mesh_instance.should_batch() could
return false in queue_prepass_material_meshes due to an unset
material_bind_group_id.

crates/bevy_pbr/src/prepass/mod.rs

@@ -851,6 +851,9 @@ pub fn queue_prepass_material_meshes<M: Material>(
                 }
             };
 
+            mesh_instance
+                .material_bind_group_id
+                .set(material.get_bind_group_id());
             match mesh_key
                 .intersection(MeshPipelineKey::BLEND_RESERVED_BITS | MeshPipelineKey::MAY_DISCARD)
             {