[tests] Include fiberNum in SimpleActorTest WDBG() log

tests/SimpleActorTest.cpp

@@ -48,10 +48,11 @@ static void mainFiber(void* runtime_ptr) {
 	sumActor.start();
 
 	CPS cps;
-	for (unsigned int i = 0; i < FIBER_COUNT; ++i) {
+	for (unsigned int fiberNum = 0; fiberNum < FIBER_COUNT; ++fiberNum) {
 		spawn(
-				[&sumActor] {
-					WDBG(Dispatcher::getCurrentFiber() << " starts to count to " << FIBERS_COUNT_TO);
+				[&sumActor, fiberNum] {
+					WDBG(Dispatcher::getCurrentFiber()
+							 << " (" << fiberNum << ") starts to count to " << FIBERS_COUNT_TO);
 					for (uint64_t i = 1; i <= FIBERS_COUNT_TO; ++i) {
 						sumActor.tell(i);
 					}