pkg/vcs: extend ListCommitHashes #14972

Job	Run time
aux	4m 53s
build	13m 2s
arch (presubmit_arch_linux)	10m 52s
dashboard	3m 33s
arch (presubmit_arch_freebsd)	6m 48s
gvisor	4m 10s
arch (presubmit_arch_netbsd)	4m 31s
old	6m 33s
arch (presubmit_arch_openbsd)	4m 29s
race	8m 55s
arch (presubmit_arch_darwin)	4m 15s
race_dashboard	4m 16s
arch (presubmit_arch_windows)	3m 27s
arch (presubmit_arch_executor)	3m 15s
	1h 22m 59s

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