Support requesting latest nightly with `tools: nightly` #4664

Job	Run time
Resolve environment (macos-latest, linked)	1m 49s
Resolve environment (ubuntu-latest, nightly-latest)	33s
Resolve environment (ubuntu-latest, default)	38s
Resolve environment (macos-latest, default)	1m 38s
Resolve environment (windows-latest, nightly-latest)	2m 29s
Resolve environment (ubuntu-latest, linked)	32s
Resolve environment (windows-latest, default)	1m 20s
Resolve environment (macos-latest, nightly-latest)	2m 26s
Resolve environment (windows-latest, linked)	1m 40s
	13m 5s

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