[neon-notifications] Dev Required: qt6-mqtt - 6.9.0-beta3

[Neon CI]

https://build.neon.kde.org/job/watcher_release_qt6_qt6-mqtt/211/display/redirect

#<Debian::UScan::DEHS::Package:0x000070ef2f8c1308 @name="qt6-mqtt", @debian_uversion="6.8.2", @debian_mangled_uversion="6.8.2", @upstream_version="6.9.0-beta3", @upstream_url="https://github.com/qt/qtmqtt/archive/refs/tags/v6.9.0-beta3.tar.gz", @status="Newer version available">