Update (or drop) the Docker image used by Flatpak job

Merged Bartłomiej Piotrowski requested to merge barthalion/gnome-runtime-images-quay into master

The gnome-runtime-images have been recently migrated to Quay. This is already reflected in the template.

Please note this MR has been created semi-automatically. If it doesn't make sense, feel free to close it.

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