core: dockerfile: allow hashes longer than 8 chars #2834

Job	Run time
frontend-tests	2m 20s
python-tests	3m 11s
deploy-docker-images (bootstrap, blueos, linux/arm/v7,linux/arm64/v8,linux/amd64)	7m 43s
deploy-docker-images (core, blueos, linux/arm/v7,linux/arm64/v8,linux/amd64)	11m 8s
deploy-raspberry-image	0s
	24m 22s

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