Fix my.cnf dependency
    
    Installation path macros are not allowed in file dependencies.
    Starting with F40, these break flatpak builds entirely because
    dnf5 only recognizes file deps in /etc, /usr/bin, and /usr/sbin,
    not /app/etc.  At this point, mariadb-connector-c-config is the
    sole provider of my.cnf.
    
    https://docs.fedoraproject.org/en-US/packaging-guidelines/#_file_and_directory_dependencies