Set danger variant and appropriate label to delete system hook

app/views/admin/hooks/edit.html.haml

@@ -13,7 +13,7 @@
       .form-actions
         %span>= f.submit _('Save changes'), class: 'btn gl-button btn-confirm gl-mr-3'
         = render 'shared/web_hooks/test_button', hook: @hook
-        = link_to _('Delete'), admin_hook_path(@hook), method: :delete, class: 'btn gl-button btn-danger float-right', data: { confirm: _('Are you sure?') }
+        = link_to _('Delete'), admin_hook_path(@hook), method: :delete, class: 'btn gl-button btn-danger float-right', aria: { label: _('Delete') }, data: { confirm: _('Are you sure?'), confirm_btn_variant: 'danger' }
 
     %hr