Specify `Accept` header for `toolcache.downloadTool` #5102

Job	Run time
Config export (windows-latest, nightly-latest)	2m 38s
Config export (macos-latest, linked)	1m 37s
Config export (ubuntu-latest, nightly-latest)	1m 2s
Config export (macos-latest, nightly-latest)	1m 17s
Config export (ubuntu-latest, linked)	1m 0s
Config export (windows-latest, linked)	2m 32s
	10m 6s

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