馃崚 FlatpakBackend: Update appstream cache before initializing
We were launching the job to update the appstream cache after initializing the backend. As a result, the updated versions were not used until the next launch of discover.
This should finally fix the version numbers shown for flatpaks on the Updates page
CCBUG: 448521 (cherry picked from commit b03673bc)
Edited by Ismael Asensio