node: remove unused error return from Attach (#27450)

node: Delete the unused error from return parameters of Node.Attach() func

ethclient/ethclient_test.go

@@ -250,7 +250,7 @@ func generateTestChain() []*types.Block {
 
 func TestEthClient(t *testing.T) {
 	backend, chain := newTestBackend(t)
-	client, _ := backend.Attach()
+	client := backend.Attach()
 	defer backend.Close()
 	defer client.Close()