Add signature to exported status (#12649)

app/services/backup_service.rb

@@ -3,6 +3,8 @@
 require 'rubygems/package'
 
 class BackupService < BaseService
+  include Payloadable
+
   attr_reader :account, :backup, :collection
 
   def call(backup)
@@ -20,7 +22,7 @@ class BackupService < BaseService
 
     account.statuses.with_includes.reorder(nil).find_in_batches do |statuses|
       statuses.each do |status|
-        item = serialize(status, ActivityPub::ActivitySerializer)
+        item = serialize_payload(status, ActivityPub::ActivitySerializer, signer: @account)
         item.delete(:'@context')
 
         unless item[:type] == 'Announce' || item[:object][:attachment].blank?