Update tests/test_custom_type_casters.cpp

Author: henryiii

tests/test_custom_type_casters.cpp

@@ -134,7 +134,8 @@ struct type_caster<other_lib::MyType> : public other_lib::my_caster {};
 } // namespace detail
 } // namespace PYBIND11_NAMESPACE
 
-// This simply is required to compile
+// This simply is required to compile, there is nothing to check at runtime
+// See PR https://github.com/pybind/pybind11/pull/4955 (compilation error due to ADL)
 namespace ADL_issue {
 template <typename OutStringType = std::string, typename... Args>
 OutStringType concat(Args &&...) {