Fix postponed transaction attesation which

produce a slot with multiple attestation for the same transaction

lib/archethic/beacon_chain/subset.ex

@@ -316,16 +316,24 @@ defmodule Archethic.BeaconChain.Subset do
        ) do
     next_time = SlotTimer.next_slot(time)
 
+    # Reduce transaction attestations to have one entry for a tx summary
+    new_slot =
+      Enum.reduce(
+        transaction_attestations,
+        %Slot{
+          subset: subset,
+          slot_time: next_time,
+          transaction_attestations: [],
+          end_of_node_synchronizations: end_of_sync
+        },
+        fn attestation, slot ->
+          {_, slot} = Slot.add_transaction_attestation(slot, attestation)
+          slot
+        end
+      )
+
     state
-    |> Map.put(
-      :current_slot,
-      %Slot{
-        subset: subset,
-        slot_time: next_time,
-        transaction_attestations: transaction_attestations,
-        end_of_node_synchronizations: end_of_sync
-      }
-    )
+    |> Map.put(:current_slot, new_slot)
     |> Map.put(:postponed, %{transaction_attestations: [], end_of_sync: []})
     |> Map.put(
       :subscribed_nodes,