fix: add lingering to rootless user tests #597

Job	Run time
lint (golangci-lint)	4s
build (nix-snapshotter)	1m 44s
build (image-hello)	1m 39s
build (image-redis)	1m 32s
build (image-redisWithShell)	1m 48s
integration-test (snapshotter)	4m 44s
integration-test (push-n-pull)	3m 53s
integration-test (kubernetes)	5m 52s
integration-test (k3s)	13m 12s
integration-test (k3s-external)	12m 38s
integration-test (k3s-rootless)	13m 0s
integration-test (gvisor)	3m 42s
coverage-report	2m 54s
	1h 6m 42s

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