incusd/instances/publish: Fix base metadata #2979

Job	Run time
Documentation	4m 33s
Code (oldstable)	2m 7s
Client (oldstable, ubuntu-latest)	1m 3s
Code (stable)	2m 2s
System (stable, cluster, dir)	4m 8s
Client (oldstable, macos-latest)	47s
Code (tip)	4m 35s
System (stable, cluster, btrfs)	2m 19s
System (stable, cluster, lvm)	4m 29s
System (stable, cluster, zfs)	3m 30s
Client (oldstable, windows-latest)	1m 21s
Client (stable, ubuntu-latest)	1m 8s
System (stable, cluster, ceph)	3m 41s
System (stable, cluster, random)	3m 6s
Client (stable, macos-latest)	52s
System (stable, standalone, dir)	3m 42s
Client (stable, windows-latest)	1m 49s
System (stable, standalone, btrfs)	4m 1s
System (stable, standalone, lvm)	2m 4s
System (stable, standalone, zfs)	3m 26s
System (stable, standalone, ceph)	2m 9s
System (stable, standalone, random)	3m 23s
System (oldstable, cluster, dir)	3m 15s
System (oldstable, standalone, dir)	3m 46s
System (tip, cluster, dir)	6m 33s
System (tip, standalone, dir)	6m 38s
	1h 20m 27s

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