Building should not require access to gitlab

In a recent commit:
46fff4d Container example updates (#88)

There is a change which a user reports now breaks their build because of a HEAD request against gitlab.

{preformat}
Use 'docker scan' to run Snyk tests against images to find vulnerabilities and learn how to fix them
examples/containers/run.sh
~/projects/cb/observability/examples/containers ~/projects/cb/observability
WARNING: Found orphan containers (exporter, couchbase-grafana) for this project. If you removed or renamed this service in your compose file, you can run this command with the --remove-orphans flag to clean it up.
Pulling couchbase-cmos (registry.gitlab.com/cb-vanilla/observability-stack:latest)...
ERROR: Head https://registry.gitlab.com/v2/cb-vanilla/observability-stack/manifests/latest: denied: access forbidden
make: *** [example-containers] Error 1{preformat}

As I believe we intend users without access to any of our private docker registries, I think this is just a bug with the recent changes.