Fix malformed HTML: missing bracket in deprecated template

wagtail/admin/templates/wagtailadmin/edit_handlers/chooser_panel.html

@@ -23,7 +23,7 @@
 
             <div class="actions">
                 {% if not field.field.required %}
-                    <button type="button" class="button action-clear button-small button-secondary">{{ field.field.widget.clear_choice_text }}</button
+                    <button type="button" class="button action-clear button-small button-secondary">{{ field.field.widget.clear_choice_text }}</button>
                 {% endif %}
                 <button type="button" class="button action-choose button-small button-secondary">{{ field.field.widget.choose_another_text }}</button>
             </div>