[neon-notifications] Dev Required: appstream - 0.15.6

[Neon CI]

https://build.neon.kde.org/job/watcher_release_backports-jammy_appstream-jammy2/148/display/redirect

#<Debian::UScan::DEHS::Package:0x00007fc014006348 @name="appstream", @debian_uversion="0.15.5", @debian_mangled_uversion="0.15.5", @upstream_version="0.15.6", @upstream_url="https://www.freedesktop.org/software/appstream/releases/AppStream-0.15.6.tar.xz", @status="Newer version available">