itest: don't modify HTLC amount in testForwardInterceptorWireRecords

The goal of the test is just to make sure that we can pick up the wire
records. With the prior bug fix, if we also modify the outgoing amount
here, the normal checks to ensure that the fee has been paid will
trigger with this larger amount, which wasn't factored in during initial
route creation.

itest/lnd_forward_interceptor_test.go

@@ -539,7 +539,7 @@ func testForwardInterceptorWireRecords(ht *lntest.HarnessTest) {
 	require.Equal(ht, []byte("test"), val)
 
 	action := routerrpc.ResolveHoldForwardAction_RESUME_MODIFIED
-	newOutgoingAmountMsat := packet.OutgoingAmountMsat + 800
+	newOutgoingAmountMsat := packet.OutgoingAmountMsat
 
 	err := bobInterceptor.Send(&routerrpc.ForwardHtlcInterceptResponse{
 		IncomingCircuitKey: packet.IncomingCircuitKey,