[CI] Registry auto-update script should ensure that package versions actually exist

[chalin]

..., this isn't currently the case: e.g., #5114 (comment)

[svrnm]

It does, because it pulls the versions from the package registries. The problem is the builder, because we make use of that version from https://pkg.go.dev/go.opentelemetry.io/collector/cmd/builder?tab=versions while we reference the releases page for downloads. That might require a "github" registry or something to check at the right place.