Support requesting latest nightly with `tools: nightly` #5084

Job	Run time
Diagnostic export (ubuntu-latest, linked)	1m 6s
Diagnostic export (ubuntu-latest, nightly-latest)	1m 5s
Diagnostic export (macos-latest, nightly-latest)	1m 1s
Diagnostic export (macos-latest, linked)	1m 37s
Diagnostic export (windows-latest, nightly-latest)	2m 58s
Diagnostic export (windows-latest, linked)	2m 4s
	9m 51s

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