CI: Enable gem and golang cache for tests in `verify` stage

What does this Merge Request do and why?

Tests executed in the verify stage doesn't follow the "vendored bundle install" pattern, which is usually the default way to cache dependencies.

There is another way to do that, which relies on caching the main folder in the "GEM PATHS". This has the added benefit that doesn't require any change in how bundle is run, which is ideal for the type of tests we want to cache.

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.