This also aligns it a bit more with the Flathub build
description.
It also builds more dependencies from main or master
branches, especially GNOME ones. That should allow (a)
future breaking changes be found early, and (b) to let
the Flatpak build description sit otherwise with less
maintenance for simple version bumps.
Signed-off-by: Markus Göllnitz <camelcasenick@bewares.it>
Part-of: <https://gitlab.gnome.org/GNOME/calls/-/merge_requests/792>
