fix: insert alert before modal-header

Some blocks hide modal-header div to insert custom-tabs, so injecting
alert inside modal-header does not work. Injecting it before this header
works for all cases.

cms/static/js/views/modals/edit_xblock.js

@@ -76,7 +76,7 @@ function($, _, Backbone, gettext, BaseModal, ViewUtils, XBlockViewUtils, XBlockE
         },
 
         createWarningToast: function(upstreamLink) {
-            this.$('.modal-window-alerts').html(this.loadTemplate('edit-upstream-alert')({
+            this.$('.modal-header').before(this.loadTemplate('edit-upstream-alert')({
                 upstreamLink: upstreamLink,
             }));
         },

cms/templates/js/basic-modal.underscore

@@ -5,8 +5,6 @@
     <div class="modal-window <%- viewSpecificClasses %> modal-<%- size %> modal-type-<%- type %>" tabindex="-1" aria-labelledby="modal-window-title">
         <div class="<%- name %>-modal">
             <div class="modal-header">
-                <div class="modal-window-alerts">
-                </div>
                 <h2 id="modal-window-title" class="title modal-window-title">
                     <%- title %>
                     <% if (modalSRTitle) { %>