fix test_cost_tracker_ok_add_two_diff_accounts

cost-model/src/cost_tracker.rs

@@ -610,7 +610,7 @@ mod tests {
             testee.add_transaction_cost(CostModel::writable_accounts_iter(&tx2), &tx_cost2);
         }
         assert_eq!(cost1 + cost2, testee.block_cost);
-        assert_eq!(2, testee.cost_by_writable_accounts.len());
+        assert_eq!(4, testee.cost_by_writable_accounts.len());
         let (_ccostliest_account, costliest_account_cost) = testee.find_costliest_account();
         assert_eq!(std::cmp::max(cost1, cost2), costliest_account_cost);
     }