ReactiveStreamsTests.verifyFluxMessageChannelRestart as @RetryingTest

**Auto-cherry-pick to `7.0.x`**

Author: artembilan

spring-integration-core/src/test/java/org/springframework/integration/dsl/reactivestreams/ReactiveStreamsTests.java

@@ -278,7 +278,7 @@ void messageProducerIsNotStartedAutomatically() {
 	@Autowired
 	ConfigurableApplicationContext applicationContext;
 
-	@Test
+	@RetryingTest(10)
 	void verifyFluxMessageChannelRestart() {
 		for (long i = 0; i < 3L; i++) {
 			assertThat(this.fromPublisherResult.receive(10_000)).extracting(Message::getPayload).isEqualTo(i);