Explicitly return true when running gdk

What does this Merge Request do and why?

A recent refactor resulted in an ugly Ruby error trace when running the gdk command on its own. This MR:

• Fixes the bug
• Adds missing specs
• Runs gdk command part of verify:* CI jobs

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.

Closes #1216 (closed)