Fix typo in release cloudbuild.yaml docker image (#52)

Author: aabmass

cloudbuild.yaml

@@ -32,4 +32,4 @@ logsBucket: gs://opentelemetry-ops-e2e-cloud-build-logs
 options:
   dynamic_substitutions: true
 substitutions:
-  _TEST_RUNNER_IMAGE_NAME: us-central1-docker.pkg.dev/${PROJECT_ID}/e2e-testing/opentelemetry-operations-e2e-testing:latest
+  _TEST_RUNNER_IMAGE_NAME: us-central1-docker.pkg.dev/${PROJECT_ID}/e2e-testing/opentelemetry-operations-e2e-testing