Fix error in migration to populate historical vulnerability statistics

ee/changelogs/unreleased/238456-fix-broken-populate-vulnerability-statistics-migrations.yml

+---
+title: Fix error in migration to populate historical vulnerability statistics
+merge_request: 40835
+author:
+type: fixed

ee/lib/ee/gitlab/background_migration/populate_vulnerability_historical_statistics.rb

@@ -5,7 +5,10 @@ module EE
     module BackgroundMigration
       # This class creates/updates those project historical vulnerability statistics
       # that haven't been created nor initialized.
-      class PopulateVulnerabilityHistoricalStatistics
+      module PopulateVulnerabilityHistoricalStatistics
+        extend ::Gitlab::Utils::Override
+
+        override :perform
         def perform(project_ids)
           project_ids.each do |project_id|
             upsert_vulnerability_historical_statistics(project_id)

ee/spec/lib/ee/gitlab/background_migration/populate_vulnerability_historical_statistics_spec.rb

@@ -2,7 +2,7 @@
 
 require 'spec_helper'
 
-RSpec.describe EE::Gitlab::BackgroundMigration::PopulateVulnerabilityHistoricalStatistics, schema: 2020_08_21_224343 do
+RSpec.describe Gitlab::BackgroundMigration::PopulateVulnerabilityHistoricalStatistics, schema: 2020_08_21_224343 do
   let(:users) { table(:users) }
   let(:namespaces) { table(:namespaces) }
   let(:vulnerabilities) { table(:vulnerabilities) }

lib/gitlab/background_migration/populate_vulnerability_historical_statistics.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module BackgroundMigration
+    # This class creates/updates those project historical vulnerability statistics
+    # that haven't been created nor initialized. It should only be executed in EE.
+    class PopulateVulnerabilityHistoricalStatistics
+      def perform(project_ids)
+      end
+    end
+  end
+end
+
+Gitlab::BackgroundMigration::PopulateVulnerabilityHistoricalStatistics.prepend_if_ee('EE::Gitlab::BackgroundMigration::PopulateVulnerabilityHistoricalStatistics')