incusd: Update for math/rand deprecation #90

Job	Run time
Documentation tests	9m 5s
Code tests	8m 28s
Client tests (1.20.x, ubuntu-latest)	39s
System tests (1.20.x, cluster, dir)	12m 23s
Client tests (1.20.x, macos-latest)	54s
System tests (1.20.x, cluster, btrfs)	13m 5s
Client tests (1.20.x, windows-latest)	5m 44s
System tests (1.20.x, cluster, lvm)	13m 19s
System tests (1.20.x, cluster, zfs)	13m 17s
System tests (1.20.x, cluster, ceph)	18m 49s
System tests (1.20.x, cluster, random)	13m 56s
System tests (1.20.x, standalone, dir)	9m 5s
System tests (1.20.x, standalone, btrfs)	8m 35s
System tests (1.20.x, standalone, lvm)	9m 29s
System tests (1.20.x, standalone, zfs)	8m 10s
System tests (1.20.x, standalone, ceph)	21m 6s
System tests (1.20.x, standalone, random)	8m 15s
System tests (stable, cluster, dir)	11m 57s
System tests (stable, standalone, dir)	7m 59s
System tests (tip, cluster, dir)	12m 42s
System tests (tip, standalone, dir)	7m 56s
	3h 34m 53s

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