Support requesting latest nightly with `tools: nightly` #5086

Job	Run time
Diagnostic export (windows-latest, nightly-latest)	2m 29s
Diagnostic export (macos-latest, linked)	59s
Diagnostic export (ubuntu-latest, linked)	38s
Diagnostic export (ubuntu-latest, nightly-latest)	1m 4s
Diagnostic export (windows-latest, linked)	1m 40s
Diagnostic export (macos-latest, nightly-latest)	1m 4s
	7m 54s

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