Use exit code 0 when everything is ok

Why is this change being made?

The scanner update automation currently uses abort to exit early, which exits with a non-zero status code. This makes sense in some cases, but it is used in some scenarios which are not indicative of a failure. This leads to misleading CI status icons, which may prompt investigation even when there is no failure.

For example, https://gitlab.com/gitlab-org/security-products/analyzers/container-scanning/-/pipelines/486848951 passed with warnings, but it's actually because there is no scanner update available, which should be a regular occurrence.