status: Fix status incompatibility introduced by #6919 and move non-regeneratable proto code into /testdata #12410

Job	Run time
vet-proto	19s
tests (vet, 1.22)	2m 21s
tests (extras, 1.22)	2m 49s
tests (tests, 1.22)	3m 44s
tests (tests, 1.22, -race)	5m 31s
tests (tests, 1.22, -race -tags=buffer_pooling)	5m 37s
tests (tests, 1.22, 386)	4m 39s
tests (tests, 1.22, arm64)	6m 28s
tests (tests, 1.21)	3m 53s
tests (tests, 1.22, -race, GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=true)	5m 30s
	40m 51s

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