Unquarantine purchase CI e2e tests

What does this MR do and why?

• Unquarantine CI test since #345674 (closed) is fixed

• Update test to use top-level group UI creation on staging

Screenshots or screen recordings

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How to set up and validate locally

Run

bundle exec bin/qa Test::Instance::All https://staging.gitlab.com -- qa/specs/features/ee/browser_ui/fulfillment/purchase/purchase_ci_spec.rb

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.