[5.0.x] Fixed HTML code snippet in Tutorial's part 7 when customizing the admin's site header.

Backport of 5b52376d9f55fa7889f39225e6035c6d69168b71 from main

docs/intro/tutorial07.txt

@@ -367,7 +367,7 @@ a section of code like:
 .. code-block:: html+django
 
     {% block branding %}
-    <div id="site-name"><a href="{% url 'admin:index' %}">Polls Administration</a><div>
+    <div id="site-name"><a href="{% url 'admin:index' %}">Polls Administration</a></div>
     {% endblock %}
 
 We use this approach to teach you how to override templates. In an actual