Update test with multiple placeholders added

It wasn’t possible to test for this before because the order of
placeholders was non-deterministic. The order has been made
deterministic in https://github.com/alphagov/notifications-utils/pull/674

app/templates/components/list.html

@@ -10,6 +10,6 @@
   {{ variables | formatted_list(
     before_each="<code>",
     after_each='</code>',
-    separator=' '
+    separator=', '
   ) }}
 {%- endmacro %}