Page must have one main landmark

https://dequeuniversity.com/rules/axe/4.3/landmark-one-main

bookwyrm/templates/layout.html

@@ -206,7 +206,7 @@
 </div>
 {% endif %}
 
-<div class="section is-flex-grow-1">
+<main class="section is-flex-grow-1">
     <div class="container">
         {# almost every view needs to know the user shelves #}
         {% with request.user.shelf_set.all as user_shelves %}
@@ -214,7 +214,7 @@
         {% endblock %}
         {% endwith %}
     </div>
-</div>
+</main>
 
 <div role="region" aria-live="polite" id="live-messages">
     <p id="status-success-message" class="live-message is-sr-only is-hidden">{% trans "Successfully posted status" %}</p>