test(bigtable): alter keyring location for tests (#4182)

 bigtable requires specific locations for CMEK
diff --git a/internal/kokoro/continuous.sh b/internal/kokoro/continuous.sh
index bad7029..1b6b670 100755
--- a/internal/kokoro/continuous.sh
+++ b/internal/kokoro/continuous.sh
@@ -34,7 +34,7 @@
 export GCLOUD_TESTS_GOLANG_FIRESTORE_PROJECT_ID=gcloud-golang-firestore-tests
 export GCLOUD_TESTS_GOLANG_FIRESTORE_KEY=$KOKORO_KEYSTORE_DIR/72523_go_firestore_integration_service_account
 export GCLOUD_TESTS_API_KEY=`cat $KOKORO_KEYSTORE_DIR/72523_go_gcloud_tests_api_key`
-export GCLOUD_TESTS_GOLANG_KEYRING=projects/dulcet-port-762/locations/us/keyRings/go-integration-test
+export GCLOUD_TESTS_GOLANG_KEYRING=projects/dulcet-port-762/locations/us-central1/keyRings/go-integration-test
 export GCLOUD_TESTS_GOLANG_PROFILER_ZONE="us-west1-b"
 
 # Bigtable integration tests expect an existing instance and cluster