Use the recently-added X-Flatpak desktop key to avoid using a heuristic

1 job for <span class="ref-name">wip/hughsie/flatpak-to-desktop-or-not</span> in 3 minutes and 48 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #126368
build-gnome-software

00:03:48