fix: add lingering to rootless user tests #599

Job	Run time
lint (golangci-lint)	2s
build (nix-snapshotter)	1m 29s
build (image-hello)	1m 31s
build (image-redis)	1m 55s
build (image-redisWithShell)	2m 21s
integration-test (snapshotter)	4m 47s
integration-test (push-n-pull)	3m 49s
integration-test (kubernetes)	4m 48s
integration-test (k3s)	12m 21s
integration-test (k3s-external)	12m 48s
integration-test (k3s-rootless)	12m 37s
integration-test (gvisor)	2m 55s
coverage-report	3m 1s
	1h 4m 24s

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