Ubuntu distro didn't raise the error for installing mariadb over container namespace

When running mariadb process in the container the process is created in isolated namespace.
MDEV-21331 explained the error that happens on Debian and this is expected situation.
Problem is that on Ubuntu distro (tested with bionic) we don't get the same situation; so installing mariadb on a host system over started container will not raise the error.

# Start container (no mariadb server installed)

$ docker container run --rm --name mysql-cont -e MYSQL_ROOT_PASSWORD=secret -d mysql

# Install mariadb on a host

$ sudo apt install mariadb-server-10.2 # version 10.2.31 (use archive.mariadb.org)

# The last command should fail prior 10.2.31, but on Ubuntu is not failing