fix: test tweaks

Author: georgeroman

src/OpReceiverProxy.sol

@@ -14,9 +14,7 @@ contract OpReceiverProxy is ERC20, Utils {
 
     // Constants
 
-    address public constant OP_GATEWAY =
-        0x99C9fc46f92E8a1c0deC1b1747d010903E884bE1;
-
+    address public immutable OP_GATEWAY;
     uint32 public immutable SENDER_CHAIN_ID;
     address public immutable HYPERLANE_MAILBOX;
     uint256 public immutable FEE_BPS;
@@ -30,11 +28,13 @@ contract OpReceiverProxy is ERC20, Utils {
     // Constructor
 
     constructor(
+        address _opGateway,
         uint32 _senderChainId,
         address _hyperlaneMailbox,
         uint256 _feeBps,
         address _opSenderProxy
     ) {
+        OP_GATEWAY = _opGateway;
         SENDER_CHAIN_ID = _senderChainId;
         HYPERLANE_MAILBOX = _hyperlaneMailbox;
         FEE_BPS = _feeBps;

test/OpReceiverProxyTest.sol

@@ -3,17 +3,15 @@ pragma solidity ^0.8.28;
 import {Test} from "forge-std/Test.sol";
 
 import {HyperlaneMailboxMock} from "./mocks/HyperlaneMailboxMock.sol";
-import {OpBridgeMock} from "./mocks/OpBridgeMock.sol";
 import {OpReceiverProxy} from "../src/OpReceiverProxy.sol";
 import {IHyperlaneMailbox} from "../src/interfaces/IHyperlaneMailbox.sol";
-import {IOpBridge} from "../src/interfaces/IOpBridge.sol";
 
 contract OpReceiverProxyTest is Test {
     address public user;
 
-    IOpBridge public opBridge;
     IHyperlaneMailbox public hyperlaneMailbox;
 
+    address public opGateway;
     uint32 public senderChainId;
     uint256 public feeBps;
     address public opSenderProxy;
@@ -24,14 +22,15 @@ contract OpReceiverProxyTest is Test {
         user = address(1);
         vm.deal(user, 1000 ether);
 
-        opBridge = new OpBridgeMock();
         hyperlaneMailbox = new HyperlaneMailboxMock();
 
+        opGateway = address(2);
         senderChainId = 1;
         feeBps = 5e15;
         opSenderProxy = address(2);
 
         opReceiverProxy = new OpReceiverProxy(
+            opGateway,
             senderChainId,
             address(hyperlaneMailbox),
             feeBps,