group: iterator_concept

src/entt/entity/group.hpp

@@ -44,6 +44,7 @@ public:
     using pointer = input_iterator_pointer<value_type>;
     using reference = value_type;
     using iterator_category = std::input_iterator_tag;
+    using iterator_concept = std::forward_iterator_tag;
 
     constexpr extended_group_iterator()
         : it{},