Update testing documentation referencing SuperchainWETH (ethereum-optimism#15476)

* Update testing.md

* Update testing.md

* Update testing.md

* Update testing.md

Author: zeevick10

devnet-sdk/book/src/testing.md

@@ -85,8 +85,8 @@ func wrapETHScenario(chainIdx uint64, walletGetter validators.WalletGetter) syst
         user := walletGetter(ctx)
 
         // Access contract registry
-        wethAddr := constants.SuperchainWETH
-        weth, err := chain.ContractsRegistry().SuperchainWETH(wethAddr)
+        wethAddr := constants.WETH
+        weth, err := chain.ContractsRegistry().WETH(wethAddr)
         require.NoError(t, err)
 
         // Test logic using pure interfaces