[3.4] release: use GitHub's gh to create GitHub release #15568

Job	Run time
test (linux-amd64-fmt)	55s
test (linux-amd64-integration-1-cpu)	9m 53s
test (linux-amd64-integration-2-cpu)	9m 54s
test (linux-amd64-integration-4-cpu)	9m 34s
test (linux-amd64-functional)	7m 59s
test (linux-amd64-unit-4-cpu-race)	52s
test (all-build)	3m 36s
test (linux-amd64-grpcproxy)	15m 15s
test (linux-amd64-e2e)	14m 2s
test (linux-386-unit)	42s
	1h 12m 42s

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