incusd/auth/openfga: Fix handling of cluster members #618

Job	Run time
Code	6m 33s
Documentation	8m 31s
Client (1.20.x, ubuntu-latest)	1m 3s
Client (1.20.x, macos-latest)	1m 38s
Client (1.20.x, windows-latest)	2m 33s
System (1.20.x, cluster, dir)	12m 12s
System (1.20.x, cluster, btrfs)	12m 19s
System (1.20.x, cluster, lvm)	13m 1s
System (1.20.x, cluster, zfs)	15m 17s
System (1.20.x, cluster, ceph)	17m 24s
System (1.20.x, cluster, random)	12m 48s
System (1.20.x, standalone, dir)	22m 37s
System (1.20.x, standalone, btrfs)	22m 15s
System (1.20.x, standalone, lvm)	39m 25s
System (1.20.x, standalone, zfs)	42m 29s
System (1.20.x, standalone, ceph)	1h 13m 59s
System (1.20.x, standalone, random)	24m 15s
System (stable, cluster, dir)	11m 7s
System (stable, standalone, dir)	22m 33s
System (tip, cluster, dir)	12m 20s
System (tip, standalone, dir)	22m 1s
	6h 36m 20s

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