error menu.html.twig with item class array

Problem/Motivation

the template got an issue with a specific variable: "item.url.options.attributes.class"
(file : dsfr/templates/navigation/menu.html.twig line 138)

The data saved can be an array instead a string.

Steps to reproduce

install "menu link attributes" module, edit a menu and add a class attribute

Proposed resolution

Test if the variable "item.url.options.attributes.class" is a string or an array.