Fix issue with MessagesController (base html) - error type (#10281)

The success type was used twice so there was no way to add an error message. See #10182.

wagtail/admin/templates/wagtailadmin/base.html

@@ -32,7 +32,7 @@
                 <template data-w-messages-target="template" data-type="success">
                     <li class="success">{% icon name="success" classname="messages-icon" %}<span></span></li>
                 </template>
-                <template data-w-messages-target="template" data-type="success">
+                <template data-w-messages-target="template" data-type="error">
                     <li class="error">{% icon name="warning" classname="messages-icon" %}<span></span></li>
                 </template>
                 <template data-w-messages-target="template" data-type="warning">