Merge branch 'fix/import-export-build-token' into 'master'

Fix duplicated build token problem importing projects

Reset token so duplicated builds do not thrown an error on import

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/23475

See merge request !8171

changelogs/unreleased/fix-import-export-build-token.yml

+---
+title: Fix Import/Export duplicated builds error
+merge_request: 
+author: 

lib/gitlab/import_export/relation_factory.rb

@@ -101,6 +101,8 @@ module Gitlab
       def generate_imported_object
         if BUILD_MODELS.include?(@relation_name) # call #trace= method after assigning the other attributes
           trace = @relation_hash.delete('trace')
+          @relation_hash.delete('token')
+
           imported_object do |object|
             object.trace = trace
             object.commit_id = nil

spec/lib/gitlab/import_export/project.json

@@ -6548,7 +6548,9 @@
             "url": null
           },
           "erased_by_id": null,
-          "erased_at": null
+          "erased_at": null,
+          "type": "Ci::Build",
+          "token": "abcd"
         },
         {
           "id": 72,

spec/lib/gitlab/import_export/project_tree_restorer_spec.rb

@@ -189,6 +189,14 @@ describe Gitlab::ImportExport::ProjectTreeRestorer, services: true do
           end
         end
       end
+
+      context 'when there is an existing build with build token' do
+        it 'restores project json correctly' do
+          create(:ci_build, token: 'abcd')
+
+          expect(restored_project_json).to be true
+        end
+      end
     end
   end
 end