Trying to run “sudo apt-get update” / “sudo apt-get upgrade”, and it’s failing because all these links like this return 404:

http://sfo1.mirrors.digitalocean.com/mariadb/repo/10.4/ubuntu/pool/main/m/mariadb-10.4/mysql-common_10.4.9+maria~bionic_all.deb

Where can I find these files, and how can I tell my update/upgrade commands to point to the correct URLs?