Fix(subscribable banner): more explicit testing

What does this MR do?

This MR is a follow-up to this MR: !51705 (merged) creating more explicit tests for the change.

Screenshots (strongly suggested)

Renew	Upgrade

Self managed

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

Requires:

• Customers app set up an running

• bundle exec rails c and run:

> Feature.enable(:subscribable_subscription_banner)
> group = Group.find_by_full_path('h5bp')
> subscription = GitlabSubscription.where(namespace_id: group.id)[0]
> subscription.update(end_date: Date.current - 1.week, trial_ends_on: Date.current - 1.week)

• Navigate to http://localhost:3000/h5bp and click "Renew" in the banner (make sure you are already logged into the customers' app!)
• It should display the renew page with your subscription

> subscription.update(end_date: Date.current - 3.week, trial_ends_on: Date.current - 3.week)

• Navigate to http://localhost:3000/h5bp and click "Upgrade"
• It should navigate you to the customers' app general /subscriptions page

In order to test the user:

• set export GITLAB_LICENSE_MODE='test' in your gdk env.runit-file
• run gdk reconfigure
• Navigate to http://localhost:3000/admin/license
• Upload this license: Will_expire_soon.gitlab-license
• Navigate to http://localhost:3000/admin, see the banner on top and click "Renew"
• It should navigate you to the customers' app general /subscriptions page

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to: https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/2499