chore: update librarian generator image builder to point to the correct location in librarian project (#14239)

Author: ldetmer

cloudbuild.yaml

@@ -24,7 +24,7 @@ steps:
       # Specifies the build context directory
       - '--context=.'
       # The final destination for the image
-      - '--destination=gcr.io/$PROJECT_ID/python-librarian-generator:latest'
+      - '--destination= us-central1-docker.pkg.dev/cloud-sdk-librarian-prod/images-dev/python-librarian-generator:latest'
       # Enables Kaniko's remote registry caching
       - '--cache=true'
       # (Optional but recommended) Sets a time-to-live for cache layers