Fix: Skip mixing enum/reference index attributes in simulation bake

Interpolating these attributes as integer values isn't meaningful or
helpful and is potentially problematic. So far I'd guess this is unlikely
to happen in practice which is why it probably hasn't been noticed yet.

Fixes part of #129691.

Pull Request: https://projects.blender.org/blender/blender/pulls/129809

source/blender/geometry/intern/mix_geometries.cc

@@ -176,12 +176,13 @@ bke::GeometrySet mix_geometries(bke::GeometrySet a, const bke::GeometrySet &b, c
       bke::MutableAttributeAccessor a = curves_a->geometry.wrap().attributes_for_write();
       const bke::AttributeAccessor b = curves_b->geometry.wrap().attributes();
       const Array<int> index_map = create_id_index_map(a, b);
-      mix_attributes(a,
-                     b,
-                     index_map,
-                     bke::AttrDomain::Point,
-                     factor,
-                     {"handle_type_left", "handle_type_right"});
+      mix_attributes(
+          a,
+          b,
+          index_map,
+          bke::AttrDomain::Point,
+          factor,
+          {"curve_type", "nurbs_order", "knots_mode", "handle_type_left", "handle_type_right"});
     }
   }
   if (bke::Instances *instances_a = a.get_instances_for_write()) {
@@ -193,7 +194,7 @@ bke::GeometrySet mix_geometries(bke::GeometrySet a, const bke::GeometrySet &b, c
                      index_map,
                      bke::AttrDomain::Instance,
                      factor,
-                     {});
+                     {".reference_index"});
     }
   }
   return a;