merge #513 into opencontainers/umoci:main #1094

Job	Run time
linux-ci-image	6m 37s
validate	1m 55s
macos	1m 13s
integration (opensuse/leap:latest)	14m 28s
unit	2m 17s
integration (centos:latest)	21m 37s
integration (debian:latest)	14m 19s
integration (ubuntu:latest)	9m 0s
integration (fedora:latest)	19m 16s
coverage	24s
	1h 31m 6s

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