Skip orphaned pool repositories on restore

- Instead of scheduling them, leave them in their
  orphaned state.
- Prevents restore process from breaking when they're
  encountered.

Relates to https://gitlab.com/gitlab-org/gitlab/issues/221296

changelogs/unreleased/221296-skip_orphaned_pool_repositories_on_restore.yml

+---
+title: Skip orphaned pool repositories on restore
+merge_request: 54112
+author:
+type: fixed

lib/backup/repositories.rb

@@ -201,7 +201,12 @@ module Backup
       PoolRepository.includes(:source_project).find_each do |pool|
         progress.puts " - Object pool #{pool.disk_path}..."
 
-        pool.source_project ||= pool.member_projects.first.root_of_fork_network
+        pool.source_project ||= pool.member_projects.first&.root_of_fork_network
+        unless pool.source_project
+          progress.puts " - Object pool #{pool.disk_path}... " + "[SKIPPED]".color(:cyan)
+          next
+        end
+
         pool.state = 'none'
         pool.save
 

spec/lib/backup/repositories_spec.rb

@@ -230,6 +230,16 @@ RSpec.describe Backup::Repositories do
         expect(pool_repository).not_to be_failed
         expect(pool_repository.object_pool.exists?).to be(true)
       end
+
+      it 'skips pools with no source project, :sidekiq_might_not_need_inline' do
+        pool_repository = create(:pool_repository, state: :obsolete)
+        pool_repository.update_column(:source_project_id, nil)
+
+        subject.restore
+
+        pool_repository.reload
+        expect(pool_repository).to be_obsolete
+      end
     end
 
     it 'cleans existing repositories' do