Fix original account being unfollowed on migration before the follow request could be sent (#21957)

app/workers/activitypub/migrated_follow_delivery_worker.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+class ActivityPub::MigratedFollowDeliveryWorker < ActivityPub::DeliveryWorker
+  def perform(json, source_account_id, inbox_url, old_target_account_id, options = {})
+    super(json, source_account_id, inbox_url, options)
+    unfollow_old_account!(old_target_account_id)
+  end
+
+  private
+
+  def unfollow_old_account!(old_target_account_id)
+    old_target_account = Account.find(old_target_account_id)
+    UnfollowService.new.call(@source_account, old_target_account, skip_unmerge: true)
+  rescue StandardError
+    true
+  end
+end