Update promote.sh to switch to prerelease #2784

Job	Run time
Documentation / Build, test & deploy	7m 17s
CI / Lint	1m 53s
CI / Build	2m 12s
CI / Build demo app	2m 18s
CI / Unit tests	3m 34s
CI / Integration tests (0)	3m 13s
CI / Integration tests (1)	3m 43s
CI / Integration tests (2)	3m 38s
CI / Integration tests (4)	3m 39s
CI / Integration tests (3)	3m 43s
Deploy release	2m 30s
	37m 40s

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