There's no such thing as an account with or without login permissions. Normally you need a git account. And that means you can log in to it. You can use ForceCommand to make it so you can only run the git server, but if a mistake is made with this configuration then you can log in or port forward or X forward or file transfer as git.
If we are going to be clever we should follow the statistics and go for 12 that where not on the toplist!!
12 - Rank 318
21 - Rank 523
I'm surprised that '12' is so low on the list.
It is a common username (see: https://en.wikipedia.org/wiki/Toor_(Unix) ), the machine I am typing this on has it.