Reinstate disabled Reactor Netty test

Reinstate test now that we are on a reactor-netty releases that fixes
reactor/reactor-netty issue 1093.

Closes gh-21437

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/embedded/netty/NettyReactiveWebServerFactoryTests.java

@@ -21,7 +21,6 @@
 import java.util.Arrays;
 
 import org.awaitility.Awaitility;
-import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 import org.mockito.InOrder;
 import reactor.core.publisher.Mono;
@@ -126,11 +125,6 @@ void whenServerIsShuttingDownGracefullyThenNewConnectionsCannotBeMade() throws E
 		this.webServer.stop();
 	}
 
-	@Disabled("Flaky due to https://github.com/reactor/reactor-netty/issues/1093")
-	@Override
-	protected void whenARequestRemainsInFlightThenShutDownGracefullyDoesNotInvokeCallbackUntilTheRequestCompletes() {
-	}
-
 	protected Mono<String> testSslWithAlias(String alias) {
 		String keyStore = "classpath:test.jks";
 		String keyPassword = "password";

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/reactive/server/AbstractReactiveWebServerFactoryTests.java

@@ -359,7 +359,7 @@ void whenThereAreNoInFlightRequestsShutDownGracefullyReturnsTrueBeforePeriodElap
 	}
 
 	@Test
-	protected void whenARequestRemainsInFlightThenShutDownGracefullyDoesNotInvokeCallbackUntilTheRequestCompletes()
+	void whenARequestRemainsInFlightThenShutDownGracefullyDoesNotInvokeCallbackUntilTheRequestCompletes()
 			throws Exception {
 		AbstractReactiveWebServerFactory factory = getFactory();
 		factory.setShutdown(Shutdown.GRACEFUL);