I've updated a 13.0.5 installation and it worked. The issue I don't like is that the first person who connects to the web interface has to push the "start upgrade" button or whatever it was called. This could be anyone from the user base, not just the sysadmin, as no login is required. It really would be best if we could completely bypass this step so it did the upgrade at the time of the installation. I looks like the upgrade() function is called from /home/devel/apps/nextcloud/nextcloud/core/ajax/update.php but I can't help much more.