pkg/vcs: extend ListCommitHashes #14973

Job	Run time
build	13m 32s
aux	4m 50s
arch (presubmit_arch_linux)	10m 47s
dashboard	3m 25s
arch (presubmit_arch_freebsd)	6m 42s
gvisor	4m 23s
old	6m 35s
arch (presubmit_arch_netbsd)	4m 22s
arch (presubmit_arch_openbsd)	4m 19s
race	8m 11s
race_dashboard	4m 37s
arch (presubmit_arch_darwin)	4m 15s
arch (presubmit_arch_windows)	3m 19s
arch (presubmit_arch_executor)	3m 13s
	1h 22m 30s

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