Refactor code around transaction

Extract transaction

ee/lib/gitlab/background_migration/migrate_approver_to_approval_rules.rb

@@ -98,6 +98,7 @@ module Gitlab
 
         raise "Incorrect target_type #{target_type}" unless ALLOWED_TARGET_TYPES.include?(@target_type)
 
+        ActiveRecord::Base.transaction do
           case target
           when MergeRequest
             handle_merge_request
@@ -105,24 +106,21 @@ module Gitlab
             handle_project
           end
         end
+      end
 
       private
 
       def handle_merge_request
-        ActiveRecord::Base.transaction do
         if rule = sync_rule
           rule.approval_project_rule = target.target_project.approval_rules.regular.first
         end
 
         target.sync_code_owners_with_approvers
       end
-      end
 
       def handle_project
-        ActiveRecord::Base.transaction do
         sync_rule
       end
-      end
 
       def sync_rule
         unless approvers_exists?