add checkout to docker-cleanup #152

Job	Run time
build-docker-normal / build-docker-image (riscv64)	24m 47s
build-docker-normal / build-docker-image (s390x)	24m 15s
build-docker-normal / build-docker-image (arm64)	24m 20s
build-docker-normal / build-docker-image (arm/v7)	23m 1s
build-docker-normal / build-docker-image (amd64)	2m 57s
build-docker-normal / build-docker-image (ppc64le)	25m 27s
build-docker-normal / merge	20s
build-docker-minimal / build-docker-image (s390x)	26s
build-docker-minimal / build-docker-image (arm/v7)	24m 37s
build-docker-minimal / build-docker-image (riscv64)	27s
build-docker-minimal / build-docker-image (arm64)	23s
build-docker-minimal / build-docker-image (amd64)	2m 45s
build-docker-minimal / build-docker-image (ppc64le)	25s
build-docker-minimal / merge	23s
	2h 34m 33s

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