Explicitly set class name for relation in migrations

lib/gitlab/background_migration/populate_missing_vulnerability_dismissal_information.rb

@@ -10,7 +10,7 @@ module Gitlab
 
         self.table_name = 'vulnerabilities'
 
-        has_one :finding
+        has_one :finding, class_name: '::Gitlab::BackgroundMigration::PopulateMissingVulnerabilityDismissalInformation::Finding'
 
         scope :broken, -> { where('state = 2 AND (dismissed_at IS NULL OR dismissed_by_id IS NULL)') }