Fix follow requests which get stuck pending
Recipients of the bad activity have Oban job failures that look like this:
** (Oban.PerformError) Pleroma.Workers.ReceiverWorker failed with {:cancel, {:error, #Ecto.Changeset<action: :insert, changes: %{id: "https://friedcheese.us/activities/a8a00bb6-fe24-4f16-afb7-396b3785ba5c", type: "Follow", to: ["https://bikeshed.party/users/feld"], actor: "https://friedcheese.us/users/feld", object: "https://bikeshed.party/users/feld"}, errors: [cc: {"can't be blank", [validation: :required]}], data: #Pleroma.Web.ActivityPub.ObjectValidators.FollowValidator<>, valid?: false>}}