[Do not merge] Specify `Accept` header for `toolcache.downloadTool` #1384

Job	Run time
Upload debug artifacts (nightly-latest)	6m 18s
Upload debug artifacts (linked)	6m 42s
Upload debug artifacts (stable-v2.20.3)	6m 2s
Upload debug artifacts (default)	6m 57s
Download and check debug artifacts	5s
	26m 4s

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