Show the conflicted diff only in ee-specific-lines-check

There's another case where it shouldn't conflict but conflicted in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6376, which gave: https://gitlab.com/gitlab-org/gitlab-ee/-/jobs/80330885

I tried to run the same rebasing command locally:

git rebase --onto fbaaa5743149395cacd02f7651971347bb404a43 a7bc7940a0f2ebc57994661a982ecb44894d1ee1 target-ce/update-rubocop

And now I see that actually only app/models/ci/build_trace_chunk.rb contained a simple conflict, which I should have already resolved in the merge request.

There must have some way to pick the conflict resolution, and we should only print the conflicted diff to reduce noise.