Specify `Accept` header for `toolcache.downloadTool` #5695

Job	Run time
Ruby analysis (ubuntu-latest, nightly-latest)	47s
Ruby analysis (macos-latest, linked)	1m 18s
Ruby analysis (macos-latest, nightly-latest)	1m 17s
Ruby analysis (ubuntu-latest, default)	53s
Ruby analysis (ubuntu-latest, linked)	48s
Ruby analysis (macos-latest, default)	1m 1s
	6m 4s

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