Fix restoring associations with import/export
What does this MR do?
This MR fixes restoring some associations with import/export feature.
See https://gitlab.com/gitlab-org/gitlab-ce/issues/38756 for more details.
Does this MR meet the acceptance criteria?
- Changelog entry added, if necessary
- Tests added for this feature/bug
- Has been reviewed by Backend
What are the relevant issue numbers?