I want to confirm that the package works without problems on a mariadb-only installation after changing the line "mysql-client" to "mysql-client|virtual-mysql-client" in debian/control.
There is no problem in installing libdbd-mysql-perl and libmysqlclient18 on a box with mariadb-{server,client}. Only mysql-client is not co-installable with mariadb-client. Since MariaDB is an drop in replacement for MySQL, no further upstream changes should be necessary. regards, meik