Updated Publisher course edit template to use correct block name for CSS

ECOM-5776

course_discovery/templates/publisher/course_edit_form.html

@@ -7,7 +7,7 @@
     {% trans "Edit Course" %}
 {% endblock title %}
 
-{% block stylesheets %}
+{% block css %}
     <link rel="stylesheet" href="{% static 'bower_components/tinymce/skins/lightgray/content.min.css' %}" type="text/x-scss">
     <link rel="stylesheet" href="{% static 'bower_components/tinymce/skins/lightgray/skin.min.css' %}" type="text/x-scss">
     {{ block.super }}