Mark installed apps to be updatable if an installed in missing
its runtime for some reasons. In pre-FlatpakTransaction world,
an app migration from runtime X to runtime Y would have rendered
an app unusable because runtime Y would not be installed
automatically by clients like gnome-software.
The goal here is that clients like gnome-software can show
those installed apps as updatable again, if such a situation
arises. The FlatpakTransaction API can automatically resolve one of
its ops to install the new runtime, provided we can mark the app
as updatable again at the first place.
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