Fix flaky setup_ai_gateway_spec.rb

What does this merge request do and why?

Fixes a flaky test in spec/tasks/setup_ai_gateway_spec.rb by removing the include GDK::Output line, which overrides this abort method in lib gdk/command.rb with GDK::Output#abort instead of using Kernel#abort.

How to set up and validate locally

bundle exec rspec './spec/lib/gdk/command_spec.rb[1:3:2:1:1,1:3:3:1:1]' './spec/tasks/setup_ai_gateway_spec.rb[1:5:1]'

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

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 an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.