Don’t reattempt insertion of already known objects

Might happen if we receive e.g. a Like before the Note arrives
in our inbox and we thus already queried the Note ourselves.

lib/pleroma/workers/receiver_worker.ex

@@ -14,6 +14,7 @@ def perform(%Job{args: %{"op" => "incoming_ap_doc", "params" => params}}) do
     else
       {:error, :origin_containment_failed} -> {:discard, :origin_containment_failed}
       {:error, {:reject, reason}} -> {:discard, reason}
+      {:error, :already_present} -> {:discard, :already_present}
       {:error, _} = e -> e
       e -> {:error, e}
     end

test/pleroma/web/federator_test.exs

@@ -132,7 +132,7 @@ test "successfully processes incoming AP docs with correct origin" do
       assert {:ok, _activity} = ObanHelpers.perform(job)
 
       assert {:ok, job} = Federator.incoming_ap_doc(params)
-      assert {:error, :already_present} = ObanHelpers.perform(job)
+      assert {:discard, :already_present} = ObanHelpers.perform(job)
     end
 
     test "successfully normalises public scope descriptors" do