Upgrade norbert to Debian

[Firefishy]

norbert twin https://hardware.openstreetmap.org/servers/horntail.openstreetmap.org/ was recently upgraded to Debian 12.

norbert should be upgraded too. We may need an hour outage for the upgrade.

[tomhughes]

I'm currently running a storage sync from norbert to horntail to bring things roughly up to date first.

[tomhughes]

Sync has now completed. Note that /var/lib/replication needs to be preserved during any upgrade.