chore: update SA used for tests (googleapis#11018)

internal/kokoro/continuous.sh

@@ -24,7 +24,7 @@
 # Nightly/$MODULE: Runs tests in a specified module. Triggered nightly.
 ##
 
-export GOOGLE_APPLICATION_CREDENTIALS=$KOKORO_KEYSTORE_DIR/72523_go_integration_service_account
+export GOOGLE_APPLICATION_CREDENTIALS="${KOKORO_GFILE_DIR}/secret_manager/go-cloud-integration-service-account"
 # Removing the GCLOUD_TESTS_GOLANG_PROJECT_ID setting may make some integration
 # tests (like profiler's) silently skipped, so make sure you know what you are
 # doing when changing / removing the next line.
@@ -34,8 +34,10 @@ export GCLOUD_TESTS_GOLANG_SECONDARY_BIGTABLE_PROJECT_ID=gcloud-golang-firestore
 export GCLOUD_TESTS_GOLANG_KEY=$GOOGLE_APPLICATION_CREDENTIALS
 export GCLOUD_TESTS_GOLANG_DATASTORE_DATABASES=database-01
 export GCLOUD_TESTS_GOLANG_FIRESTORE_PROJECT_ID=gcloud-golang-firestore-tests
+# TODO(codyoss): Update this
 export GCLOUD_TESTS_GOLANG_FIRESTORE_KEY=$KOKORO_KEYSTORE_DIR/72523_go_firestore_integration_service_account
 export GCLOUD_TESTS_GOLANG_FIRESTORE_DATABASES=database-02
+# TODO(codyoss): Update this
 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_PROFILER_ZONE="us-west1-b"