api

Simpler two queries than one JOIN with subquery

This is a follow up from !5347

Originally it was:

``` ruby
pipeline = pipelines.latest_successful_for(ref)
builds.where(pipeline: pipeline).latest.with_artifacts
```

However MySQL would complain that we can't use `IN` against a subquery which has `LIMIT`. Using `INNER JOIN` would be a workaround, however, doing that is too complicated in current version of Rails.

So let's just use two queries in this case.

Closes #14419

See merge request !5388