[neon-notifications] Dev Required: libxmlb - 0.3.21

[Neon CI]

https://build.neon.kde.org/job/watcher_release_backports-jammy_libxmlb/82/display/redirect

#<Debian::UScan::DEHS::Package:0x00007f89cfbf59b8 @name="libxmlb", @debian_uversion="0.3.15", @debian_mangled_uversion="0.3.15", @upstream_version="0.3.21", @upstream_url="https://github.com/hughsie/libxmlb/archive/refs/tags/0.3.21.tar.gz", @status="Newer version available">