pin MariaDB to 10.5

[paskalito]

https://github.com/docker-library/docs/blob/master/nextcloud/README.md

If you use the default docker compose file provided in the official desciption here and on dockerHub you will end up using a newer database than supported by nextcloud causing problems and broken databases..

pls pin it to latest supportet version 10.5

[tianon]

cc @tilosp @J0WI