feat: add unicorn flavor #964

Job	Run time
check-flavor	8s
validate (install, registry1) / run	1m 12s
validate (install, unicorn) / run	1s
validate (upgrade, registry1) / run	1s
validate (install, upstream) / run	1s
validate (upgrade, upstream) / run	1s
validate (upgrade, unicorn) / run	0s
	1m 24s

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