Provide `Authorization` header when downloading `update-job-proxy` #5158

Job	Run time
Diagnostic export (ubuntu-latest, linked)	1m 6s
Diagnostic export (macos-latest, linked)	1m 15s
Diagnostic export (windows-latest, linked)	2m 52s
Diagnostic export (ubuntu-latest, nightly-latest)	1m 8s
Diagnostic export (windows-latest, nightly-latest)	3m 44s
Diagnostic export (macos-latest, nightly-latest)	1m 20s
	11m 25s

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