Issue #3497493 by pdureau, grimreaper: Clean variant logic in templates

Closes #3497493

components/accordion/accordion.twig

-{% if variant and variant|lower != 'default' %}
-  {% set attributes = attributes.addClass('accordion-' ~ variant|lower|replace({'_': '-'})) %}
+{% if variant and variant != 'default' %}
+  {% set attributes = attributes.addClass('accordion-' ~ variant) %}
 {% endif %}
 {% set accordion_id = accordion_id|default("accordion-" ~ random()) %}
 {% set keep_open = keep_open ? 'true' : 'false' %}