OK, so 1.4.4 and friends actually enable debugging mode of unattended-upgrade instead of a download-only mode. --dry-run is documented as only doing downloads, but it also simulates the install and does verbose logging, so that's not useful.
In 1.4.6, I modified apt.systemd.daily to check unattended-upgrade --help for "download-only", and use that if it exists. This means that with 1.4.6, everything should work once this is implemented in unattended-upgrades.
I attached an early patch for unattended-upgrades (against the upstream version), there might be issues with it other than missing translations for --help.
OK, so 1.4.4 and friends actually enable debugging mode of unattended-upgrade instead of a download-only mode. --dry-run is documented as only doing downloads, but it also simulates the install and does verbose logging, so that's not useful.
In 1.4.6, I modified apt.systemd.daily to check unattended-upgrade --help for "download-only", and use that if it exists. This means that with 1.4.6, everything should work once this is implemented in unattended- upgrades.
I attached an early patch for unattended-upgrades (against the upstream version), there might be issues with it other than missing translations for --help.