[neon-notifications] Dev Required: qt6-mqtt - 6.8.0-beta4

[Neon CI]

https://build.neon.kde.org/job/watcher_release_qt6_qt6-mqtt/30/display/redirect

#<Debian::UScan::DEHS::Package:0x00007f011933ca90 @name="qt6-mqtt", @debian_uversion="6.7.2", @debian_mangled_uversion="6.7.2", @upstream_version="6.8.0-beta4", @upstream_url="https://github.com/qt/qtmqtt/archive/refs/tags/v6.8.0-beta4.tar.gz", @status="Newer version available">