[test] Call Actor.stop() in SimpleActorTest

This should not change much, but ensure that this method is also
invoked in the test (even though it is not explicitly tested).

tests/SimpleActorTest.cpp

@@ -28,6 +28,8 @@ class SumActor : public Actor<uint64_t> {
 		std::atomic_thread_fence(std::memory_order::memory_order_acquire);
 		return sum;
 	}
+
+	void stop() { Actor::stop(); }
 };
 
 static void mainFiber(void* runtime_ptr) {
@@ -62,6 +64,8 @@ static void mainFiber(void* runtime_ptr) {
 		exit(EXIT_FAILURE);
 	}
 
+	sumActor.stop();
+
 	if (sumActor.getSum() != EXPECTED_SUM) {
 		std::cerr << "FAILURE: Actor sum " << sumActor.getSum() << " is not equal to expected sum "
 							<< EXPECTED_SUM << std::endl;