Use var directly

Author: Bjorn Van Acker

templates/Form/fields.html.twig

@@ -110,7 +110,7 @@
 
     {% if allow_add %}
       <button type="button" class="btn btn-success btn-sm" data-role="collection-add-button">
-        <i class="fas fa-plus me-2"></i> {{ form.vars.add_button_label|trans|ucfirst }}
+        <i class="fas fa-plus me-2"></i> {{ add_button_label|trans|ucfirst }}
       </button>
     {% endif %}
   {% endapply %}