Cleanup subscription_spec#recurrent_subscription? tests
### Problem
Follow-up from conversation https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/12219#note_2409529972 - we should cleanup this test to only test for `has_non_renewable_duo_plans: true` once.
### Proposal
<!-- Consult with `@gitlab-com/business-technology/enterprise-apps/zuora-architects` on the ~"Enterprise Applications" team if Zuora business logic is involved. -->
### Result
### Next steps (if any)
### How will we measure success?
issue