[neon-notifications] Dev Required: libportal - 0.6

[Neon CI]

https://build.neon.kde.org/job/watcher_release_backports-focal_libportal/24/display/redirect

#<Debian::UScan::DEHS::Package:0x000056540177ca80 @name="libportal", @debian_uversion="0.4", @debian_mangled_uversion="0.4", @upstream_version="0.6", @upstream_url="https://github.com/flatpak/libportal/releases/download/0.6/libportal-0.6.tar.xz", @status="Newer version available">