The packages libmaraidbclient-dev and libmysqlclient-dev were in Conflicts with each other and not co-installable. We should probably have the same libmariadb-dev vs libmysqlclient-dev as well.
Feel free to open a merge request on Salsa for whatever change to want to have in the packaging. I wrote instructions with screenshots at https://wiki.debian.org/Teams/MySQL/patches so it would be as easy as possible to contribute. I am also grateful for meta-contributions to the contribution process itself: the wiki texts, READMEs inside the packaging, gitlab-ci.yml tweaks to make the testing more extensive and reliable etc. I made a mysql-5.7 upgrade test in the gitlab-ci.yml file (https://salsa.debian.org/mariadb-team/mariadb-10.3/blob/master/debian/gitlab-ci.yml#L138-152) but it is not enabled due to differences in auth_socket name and Password column in mysql.users table, and would for now just always fail, thus disabled. It would be very cool if you extended this file to install the libmysqlclient-dev package (and maybe some others) and then upgraded / co-installed selected MariaDB packages to verify that all d/control stanzas about conflicts/breaks/replaces are correctly working. The more bugs we can stump right at the commit they were made, the better quality we have and the better for users.
