Fixed #17234 -- Added back a missing endblock tag to an admindoc template....

Fixed #17234 -- Added back a missing endblock tag to an admindoc template. Thanks shibz for the report and fix.

Refs #16912.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17098 bcc190cf-cafb-0310-a4f2-bffc1f526a37