[neon-notifications] Releasing: kf5-messagelib - 21.04.0

[Neon CI]

https://build.neon.kde.org/job/watcher_release_kde_messagelib/1111/display/redirect

#<Debian::UScan::DEHS::Package:0x000055b015e0f680 @name="kf5-messagelib", @debian_uversion="20.12.3", @debian_mangled_uversion="20.12.3", @upstream_version="21.04.0", @upstream_url="http://download.kde.internal.neon.kde.org/stable/release-service/21.04.0/src/messagelib-21.04.0.tar.xz", @status="Newer version available">