Add code_change for subset

lib/archethic/beacon_chain/subset.ex

@@ -411,4 +411,20 @@ defmodule Archethic.BeaconChain.Subset do
   end
 
   defp ensure_p2p_view(slot = %Slot{}, _), do: slot
+
+  def code_change(
+        "1.0.7",
+        state = %{postponed: %{transaction_attestations: postponed_attestations}},
+        _extra
+      ) do
+    new_state =
+      Enum.reduce(postponed_attestations, state, fn attestation, acc ->
+        Map.update!(acc, :current_slot, &Slot.add_transaction_attestation(&1, attestation))
+      end)
+      |> Map.delete(:postponed)
+
+    {:ok, new_state}
+  end
+
+  def code_change(_, state, _), do: {:ok, state}
 end