use :discard instead of cancel

lib/pleroma/workers/receiver_worker.ex

@@ -12,8 +12,8 @@ defmodule Pleroma.Workers.ReceiverWorker do
     with {:ok, res} <- Federator.perform(:incoming_ap_doc, params) do
       {:ok, res}
     else
-      {:error, :origin_containment_failed} -> {:cancel, :origin_containment_failed}
-      {:error, {:reject, reason}} -> {:cancel, reason}
+      {:error, :origin_containment_failed} -> {:discard, :origin_containment_failed}
+      {:error, {:reject, reason}} -> {:discard, reason}
       e -> e
     end
   end