ci: Use 'pipeline::tier-3' label to decide when to run E2E dependency jobs

What does this MR do and why?

We had a case where an MR had pipelinetier-3 but was missing pipeline:mr-approved (it's really an edge case as MR should usually get both labels).

This MR ensures the dependency jobs for E2E test jobs are using the - !reference [".prevent-tier-2-and-below", rules] rule instead of

    - <<: *if-merge-request-not-approved
      when: never

Failure can be seen in https://gitlab.com/gitlab-org/gitlab/-/pipelines/1351132878

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