Merge conflicts message isn't displayed when diff_head param isn't passed
The project has `default_merge_ref_for_diffs` enabled. This merge request has conflicts: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/22505/diffs, `master (base)` version is displayed, but there's no message

One of the possible solutions would be to check here whether `default_merge_ref_for_diffs` FF is enabled: https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/diffs/components/app.vue
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issue