Fix #135432: Cycles world light and shadow catcher bug after recent changes

Caused by #134846, e813e46327.

Pull Request: https://projects.blender.org/blender/blender/pulls/135440

intern/cycles/blender/light.cpp

@@ -120,6 +120,10 @@ void BlenderSync::sync_background_light(BL::SpaceView3D &b_v3d)
       Object *object;
       const ObjectKey object_key(b_world, nullptr, b_world, false);
       bool update = object_map.add_or_update(&object, b_world, b_world, object_key);
+      if (update) {
+        /* Lights should be shadow catchers by default. */
+        object->set_is_shadow_catcher(true);
+      }
 
       /* Create geometry. */
       const GeometryKey geom_key{b_world.ptr.data, Geometry::LIGHT};