Do not federate undo->block activities

the :do_not_federate checks were omitted from the undo pipeline,
which could lead to them federating.

this commit enforces :outgoing_blocks on undos as well - and
any existing value of :do_not_federate is preserved, if one exists

Akkoma issue 957.

[Pleroma: block/unblock test calls use the Pleroma (blocked, blocker) argument order.]

(cherry picked from commit eca7ed572b8a10a0235fb1a381eac4803614dee4)

lib/pleroma/web/activity_pub/object_validator.ex

@@ -78,10 +78,16 @@ defmodule Pleroma.Web.ActivityPub.ObjectValidator do
            |> Ecto.Changeset.apply_action(:insert) do
       object = stringify_keys(object)
       undone_object = Activity.get_by_ap_id(object["object"])
+      outgoing_blocks = Pleroma.Config.get([:activitypub, :outgoing_blocks])
+      # if we're undoing a block, and do not permit federating that:
+      do_not_federate =
+        Keyword.get(meta, :do_not_federate) ||
+          (Map.get(undone_object.data, "type") == "Block" && !outgoing_blocks)
 
       meta =
         meta
         |> Keyword.put(:object_data, undone_object.data)
+        |> Keyword.put(:do_not_federate, do_not_federate)
 
       {:ok, object, meta}
     end