Improve resiliency of concurrent use the downloads directory. #1974

Job	Run time
format	2m 45s
json-schema	1m 6s
builds / build (windows-2022, windows-ci)	20m 26s
builds / build (ubuntu-20.04, linux-ci)	9m 56s
builds / build (macos-13, macos-ci)	12m 36s
	46m 49s

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