[publish-pr-preview] Not updating dependencies causes publish failure

[taras]

We noticed that builds have been failing in https://github.com/thefrontside/backstage/pull/50

After some debugging, it turned out that this is called by a dependency that is not available in the registry. Here is how it happens, Package Versions PR contains versions in dependencies for package versions that haven't been published yet. When we run publish of previews, it fails because the dependant versions haven't been published yet.

This highlights 2 problems,

1. We should be updating dependencies with versions using preview versions that we're publishing.
2. We should be publishing in order dependencies before dependents