Skip Billing Plan flaky case

What does this MR do and why?

Skip Billing Plan flaky case.

https://jihulab.com/gitlab-cn/gitlab/-/jobs/4863092

- file_path: 'ee/spec/features/billings/billing_plans_spec.rb'
  description:
    - 'Billing plan pages group billing page when a group is the top-level group on bronze when submitting hand raise lead displays the in-app hand raise lead'
  skip_reason:
    - 'skip a flaky case'

cc EM @prajnamas