Bug#1035949: mariadb: upgrade issue: mariadb-server-10.5 fails to stop after all other -10.5 packages were removed

[Otto Kekäläinen]

This is not a fix, but could help make the situation easier to
detect/debug for users:

* https://salsa.debian.org/mariadb-team/mariadb-10.5/-/merge_requests/14
* https://salsa.debian.org/mariadb-team/mariadb-10.3/-/merge_requests/37