fix: fix slice init length #2795

Job	Run time
Code (oldstable)	7m 49s
Code (stable)	7m 24s
Client (oldstable, ubuntu-latest)	31s
Documentation	5m 9s
Code (tip)	10m 30s
Client (oldstable, macos-latest)	26s
Client (oldstable, windows-latest)	55s
Client (stable, ubuntu-latest)	28s
System (stable, cluster, dir)	13m 3s
Client (stable, macos-latest)	30s
System (stable, cluster, btrfs)	14m 41s
Client (stable, windows-latest)	1m 0s
System (stable, cluster, lvm)	13m 36s
System (stable, cluster, zfs)	14m 15s
System (stable, cluster, ceph)	17m 40s
System (stable, cluster, random)	15m 35s
System (stable, standalone, dir)	22m 22s
System (stable, standalone, btrfs)	21m 18s
System (stable, standalone, lvm)	32m 33s
System (stable, standalone, zfs)	36m 33s
System (stable, standalone, ceph)	1h 14m 54s
System (stable, standalone, random)	22m 15s
System (oldstable, cluster, dir)	14m 26s
System (oldstable, standalone, dir)	22m 59s
System (tip, cluster, dir)	14m 29s
System (tip, standalone, dir)	24m 28s
	6h 49m 49s

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