Why is Homebrew running MySQL service as root and how to change it?

I used brew update brew upgrade mysql to bump version from 8.0.23 to 8.0.26 and now MySQL service won't start anymore. I try brew services start mysql and after few seconds the service status goes back to stopped. The last line in .err files in /usr/local/var/mysql says

[ERROR] [MY-010123] [Server] Fatal error: Please read "Security" section of the manual to find out how to run mysqld as root!

And when I delete the .err files they come back as owned by root. They were not owned by root before. My current user is not root and I do not use sudo to run these commands. Why is this happening and how do I fix it?