add callback back in L1ERC20GatewayValidium.finalizeWithdrawERC20 (#157)

Co-authored-by: Péter Garamvölgyi <peter@scroll.io>

Author: zimpha

src/validium/L1ERC20GatewayValidium.sol

@@ -152,6 +152,8 @@ contract L1ERC20GatewayValidium is ScrollGatewayBase, IL1ERC20GatewayValidium {
 
         IERC20Upgradeable(_l1Token).safeTransfer(_to, _amount);
 
+        _doCallback(_to, _data);
+
         emit FinalizeWithdrawERC20(_l1Token, _l2Token, _from, _to, _amount, _data);
     }