I don’t know if I could really recommend this as a standard procedure, but since I was free to crash and rebuild my own websites, I just ripped through a couple of these upgrades fast and got stuck like this on the third upgrade, and fixing it was a piece of cake.
I just ran
https://save-marriages.com/wp-admin/update-core.php
And that took care of it. (substitute your own URL)
I could see the files for the upgrade were in my wp-content/upgrade
directory, so when I ran update-core.php, it ran like lightening and I had a login screen.
From there, I just had to follow the normal instructions you get when you do this upgrade–that is, edit wp-config.php and add the specified line for security, remove blogs.php, and edit .htaccess appropriately.
Worked great. I hope this helps and does not hurt anyone.
Dan