mysqlclient 2.2 dropped support for compiling using the `mysql_config` script to locate headers/libraries, instead requiring a mysql/mariadb pkg-config file. This flat-out breaks compatibility on many systems, such as: * Alpine Linux (https://github.com/PyMySQL/mysqlclient/issues/620) * Amazon Linux (https://github.com/PyMySQL/mysqlclient/issues/634) * Debian Bookworm (https://github.com/PyMySQL/mysqlclient/issues/637) This is a pretty serious issue for users, and doesn't appear to be something the project is interested in addressing in their packaging. Unfortunately, despite the size of this imposed breakage, there's no compatibility lists anywhere for mysqlclient that we can reference and provide for our own users. Until the situation is sorted, or an alternative to mysqlclient is found/created/forked, the best we can do is cap our default `ReviewBoard[mysql]` extras package to 2.1.x, in order to preserve existing installs, and then provide a big warning and extensive instructions in our documentation.