server: add embedding requirement to ServerTransportStream #12586

Job	Run time
vet-proto	25s
vet-proto	25s
tests (vet, 1.22)	1m 35s
tests (vet, 1.22)	1m 35s
tests (extras, 1.23)	2m 49s
tests (extras, 1.23)	2m 49s
tests (tests, 1.23)	3m 51s
tests (tests, 1.23)	3m 51s
tests (tests, 1.23, -race)	5m 33s
tests (tests, 1.23, -race)	5m 33s
tests (tests, 1.23, 386)	4m 54s
tests (tests, 1.23, 386)	4m 54s
tests (tests, 1.23, arm64)	5m 45s
tests (tests, 1.23, arm64)	6m 30s
tests (tests, 1.22)	3m 18s
tests (tests, 1.22)	3m 18s
tests (tests, 1.23, -race, GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=true)	5m 32s
tests (tests, 1.23, -race, GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=true)	5m 32s
	1h 8m 9s

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