Currently if the user configures a collection ID on a remote which is
incorrect, either because it doesn't match the one configured server
side or because the server doesn't have one configured at all, Flatpak
will not notice the issue and happily still pull from the remote. This
is new since 1.7.1; before that such a problem would be caught because
the server wouldn't provide the ostree-metadata ref for the configured
collection ID.
This commit catches such errors by checking commit metadata, as we
already do for the ref binding metadata. Otherwise such a mismatch would
prevent successful offline distribution of the apps/runtimes provided by
the remote.
The impetus for this is to keep an eos-updater unit test passing with
Flatpak 1.8.x:
"/updater/install-flatpaks-pull-to-repo-error-if-collection-id-invalid"
1bf5f2ed9e