fix: fix slice init length #2796

Job	Run time
Code (oldstable)	7m 54s
Code (stable)	7m 30s
Code (tip)	10m 4s
Client (oldstable, ubuntu-latest)	28s
Client (oldstable, macos-latest)	32s
Documentation	5m 22s
System (stable, cluster, dir)	14m 7s
Client (oldstable, windows-latest)	55s
System (stable, cluster, btrfs)	12m 24s
Client (stable, ubuntu-latest)	28s
System (stable, cluster, lvm)	11m 56s
Client (stable, macos-latest)	31s
System (stable, cluster, zfs)	13m 2s
Client (stable, windows-latest)	56s
System (stable, cluster, ceph)	17m 34s
System (stable, cluster, random)	12m 3s
System (stable, standalone, dir)	22m 8s
System (stable, standalone, btrfs)	24m 8s
System (stable, standalone, lvm)	33m 19s
System (stable, standalone, zfs)	37m 42s
System (stable, standalone, ceph)	1h 13m 42s
System (stable, standalone, random)	30m 42s
System (oldstable, cluster, dir)	12m 5s
System (oldstable, standalone, dir)	22m 53s
System (tip, cluster, dir)	14m 54s
System (tip, standalone, dir)	25m 46s
	6h 53m 5s

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