Ok, uploaded. I don't guarantee that a machine currently running mariadb-server-10.3 and mariadb-server-10.3 binary packages in testing or unstable can upgrade to the latest in Buster, since the Buster has been maintained with upstream changes only, and the 10.3.x version in unstable has also had packaging fixes etc that might not be backwards compatible. Maybe just issuing a removal request in 1 week is the way to go.