Merge pull request #4619 from opensafely-core/steve/deploy-concurrency #1

Job	Run time
test-and-build-docker-image / check	40s
test-and-build-docker-image / docker-test	3m 16s
test-and-build-docker-image / lint-dockerfile	7s
test-and-build-docker-image / test	3m 7s
deploy	2m 31s
	9m 41s

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