fix: add missing block timestamp in election rewards for address response (#10907)

apps/block_scout_web/lib/block_scout_web/views/api/v2/celo_view.ex

@@ -221,11 +221,12 @@ defmodule BlockScoutWeb.API.V2.CeloView do
     }
   end
 
-  defp prepare_election_reward(%ElectionReward{token: %Token{}} = reward) do
+  defp prepare_election_reward(%ElectionReward{token: %Token{}, block: %Block{}} = reward) do
     %{
       amount: reward.amount,
       block_number: reward.block.number,
       block_hash: reward.block_hash,
+      block_timestamp: reward.block.timestamp,
       epoch_number: reward.block.number |> CeloHelper.block_number_to_epoch_number(),
       account:
         Helper.address_with_info(