Use update-prometheus-3.0 branch #15910

Job	Run time
Go build with -tags=stringlabels	53s
Check misspelled words	10s
Go build for different platforms	10m 0s
Thanos end-to-end tests (8, 0)	5m 3s
Linters (Static Analysis) for Go	3m 10s
Thanos unit tests	10m 39s
Thanos end-to-end tests (8, 1)	3m 53s
Thanos end-to-end tests (8, 2)	4m 5s
Thanos end-to-end tests (8, 3)	4m 43s
Thanos end-to-end tests (8, 4)	4m 15s
Thanos end-to-end tests (8, 5)	4m 5s
Thanos end-to-end tests (8, 6)	4m 11s
Thanos end-to-end tests (8, 7)	3m 58s
	59m 5s

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