fix(docs): hide Scarf tracking pixel to remove page whitespace (#6209)

overrides/main.html

@@ -7,6 +7,8 @@
 {% endblock %}
 
 {% block footer %}
-<img referrerpolicy="no-referrer-when-downgrade" src="https://static.scarf.sh/a.png?x-pxid=6658a9eb-067d-49f1-94f2-b8b00f21451e"  alt=""/>
+<img referrerpolicy="no-referrer-when-downgrade"
+  src="https://static.scarf.sh/a.png?x-pxid=6658a9eb-067d-49f1-94f2-b8b00f21451e" alt=""
+  hidden />
   {{ super() }}
 {% endblock %}