[neon-notifications] Dev Required: appstream - 0.15.3

[Neon CI]

https://build.neon.kde.org/job/watcher_release_backports-focal_appstream/188/display/redirect

#<Debian::UScan::DEHS::Package:0x000056021ed30ab0 @name="appstream", @debian_uversion="0.15.2", @debian_mangled_uversion="0.15.2", @upstream_version="0.15.3", @upstream_url="https://www.freedesktop.org/software/appstream/releases/AppStream-0.15.3.tar.xz", @status="Newer version available">