Add link to print class register.

biscuit/apps/alsijil/templates/alsijil/group_week.html

@@ -15,7 +15,7 @@
         {% blocktrans %}Select{% endblocktrans %}
       </button>
     </form>
-    <a class="btn btn-secondary" href="{% url 'full_register_group' id=group.id_ %}">
+    <a class="btn btn-secondary" href="{% url 'full_register_group' group.id %}">
       {% fa 'print' %}
     </a>
   </div>