Rename PSM interop fallback test suite to light #15486

Job	Run time
vet-proto	35s
tests (vet, 1.23)	1m 20s
tests (tests, 1.24)	4m 54s
tests (tests, 1.24, -race)	6m 20s
tests (extras, 1.24)	2m 56s
tests (tests, 1.24, arm64)	6m 18s
tests (tests, 1.24, 386)	5m 15s
tests (tests, 1.23)	3m 54s
tests (tests, 1.24, -race, GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=false)	6m 22s
tests (tests, 1.24)	4m 54s
tests (extras, 1.24)	2m 56s
tests (tests, 1.24, 386)	5m 15s
tests (vet, 1.23)	1m 20s
tests (tests, 1.24, arm64)	10m 36s
tests (tests, 1.24, -race, GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=false)	6m 22s
tests (tests, 1.23)	3m 54s
tests (tests, 1.24, -race)	6m 20s
vet-proto	35s
tests (tests, 1.24, arm64)	7m 10s
tests (tests, 1.24, -race)	6m 20s
tests (vet, 1.23)	1m 20s
tests (tests, 1.24)	4m 54s
tests (tests, 1.24, -race, GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=false)	6m 22s
tests (tests, 1.23)	3m 54s
tests (tests, 1.24, 386)	5m 15s
vet-proto	35s
tests (extras, 1.24)	2m 56s
	1h 58m 52s

Provide feedback