Change version to v1.71.3 #15501

Job	Run time
vet-proto	28s
tests (tests, 1.23)	4m 41s
tests (extras, 1.23)	1m 59s
tests (tests, 1.23, -race, GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=true)	6m 3s
tests (tests, 1.23, arm64)	6m 39s
tests (tests, 1.22)	4m 14s
tests (tests, 1.23, 386)	4m 52s
tests (vet, 1.22)	2m 11s
tests (tests, 1.23, -race)	6m 4s
tests (extras, 1.23)	2m 56s
tests (tests, 1.23)	4m 41s
vet-proto	28s
tests (vet, 1.22)	2m 11s
tests (tests, 1.23, arm64)	6m 39s
tests (tests, 1.23, -race)	6m 4s
tests (tests, 1.22)	4m 14s
tests (tests, 1.23, -race, GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=true)	6m 3s
tests (tests, 1.23, 386)	4m 52s
	1h 15m 19s

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