fix(tests/spanner): Fix swallowing of spanner integration test failures

This PR fixes an issue with the CI/CD setup which caused failures from spanner integration tests to be swallowed, meaning the errors were just logged and the test ran green.

This PR fixes that by updating the command needed to run the spanner test.

Author: anubhav756

.ci/integration.cloudbuild.yaml

@@ -522,7 +522,7 @@ steps:
           .ci/test_with_coverage.sh \
             "Spanner" \
             spanner \
-            spanner || echo "Integration tests failed."
+            spanner || { echo "Integration tests failed."; exit 1; }
         else
           echo "No relevant changes for Spanner. Skipping shard."
           exit 0