exporter: add tests for a directory with an idmap error #4589

Job	Run time
prepare	1s
test / prepare	2m 11s
test / run (containerd, ./frontend/dockerfile, integration)	5m 10s
test / run (containerd, ./frontend/dockerfile, dockerfile)	6m 46s
test / run (containerd-rootless, ./frontend/dockerfile, integration)	4m 45s
test / run (containerd-rootless, ./frontend/dockerfile, dockerfile)	6m 26s
test / run (containerd-1.6, ./frontend/dockerfile, integration)	4m 49s
test / run (containerd-1.6, ./frontend/dockerfile, dockerfile)	7m 1s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, integration)	5m 14s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	7m 12s
test / run (oci, ./frontend/dockerfile, integration)	4m 21s
test / run (oci, ./frontend/dockerfile, dockerfile)	5m 47s
test / run (oci-rootless, ./frontend/dockerfile, integration)	4m 21s
test / run (oci-rootless, ./frontend/dockerfile, dockerfile)	5m 44s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, integration)	4m 28s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, dockerfile)	5m 41s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, integration)	4m 29s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	5m 59s
image (mainline)	5m 10s
image (labs)	4m 58s
release	0s
scout	0s
	1h 40m 33s

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