xfce-do-release: Update Appdata file

This adds the new release to the Appdata file if the `<releases>` tag
exists. This file is only searched in the root of the repository and in
the `data` directory, and must be unique.
2 jobs for !61 with xfce-do-release-update-appdata in 49 seconds (queued for 6 seconds)
merge request