Note: it could be possible you meet some issues with dns resolution, mariadb-server and dovecot during upgrade.
A solution could be :
-
echo "nameserver 89.234.141.66" > /etc/resolv.conf(in order to fix DNS resolution temporarily during the upgrade) - uninstall manually all mariadb related package with
dpkg -r --force-depends XXXX - fake the dovecot service with a
ExecStart=/bin/true(don’t forget to do systemctl daemon-reload). - Next you can rerun the migrations
Or you can reinstall and restore your backup.