Follow-up from "BulkImports: Add PipelineWorker"

The following discussion from !57153 (merged) should be addressed:

• @alberts-gitlab started a discussion: (+3 comments)

  This should be tested in ee/spec/models/ee/bulk_imports/stage_spec.rb. https://docs.gitlab.com/ee/development/ee_features.html#testing-ee-features-based-on-ce-features.

  As it is, this test is always testing the ee behaviour because the Gitlab.ee? is always true in gitlab-org/gitlab, with the exception of [RUN AS-IF-FOSS] MRs.