NuCivic/nucivic-internal#153 Changing ref_field patch. Unlike the old on...

...e that only fix deletion cases this fix insertion cases.

NuCivic/nucivic-internal#153 

### Acceptance test
- [ ] Install dkan
- [ ] Install https://github.com/NuCivic/dkan_migrate_base
- [ ] Go to /admin/content/migrate/groups/dkan
- [ ] Run ckan_group_base migration and should no longer be displayed any warning.