Add static linter to validate Bulk Import's EE stage files
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Suggestion from https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74722#note_741382658
Whe adding new pipelines to:
- `lib/bulk_imports/projects/stage.rb`
- `lib/bulk_imports/groups/stage.rb`
We also need to add them to:
- `ee/lib/ee/bulk_imports/projects/stage.rb`
- `ee/lib/ee/bulk_imports/groups/stage.rb`
Which is not obvious and sometimes EE spec can not fail either, meaning that this will get merged unnoticed. We should either add a static linter to validate EE files, or only validate EE pipelines in EE specific specs, since CE pipelines are already validated in CE specs.
issue