fix: fix slice init length #13676

Job	Run time
build	12m 23s
aux	5m 0s
dashboard	5m 47s
arch (presubmit_arch_linux)	11m 4s
gvisor	4m 17s
old	6m 39s
arch (presubmit_arch_freebsd)	6m 47s
race	10m 6s
arch (presubmit_arch_netbsd)	4m 33s
race_dashboard	6m 52s
arch (presubmit_arch_openbsd)	4m 26s
arch (presubmit_arch_darwin)	4m 29s
arch (presubmit_arch_windows)	3m 30s
arch (presubmit_arch_executor)	3m 22s
	1h 29m 15s

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