Try to stabilize SampleSessionWebFluxApplicationTests

userDefinedMappingsSecureByDefault in
SampleSessionWebFluxApplicationTests may fail with an NPE if the
session times out before the initial response is sent due to the absence
of a SESSION cookie in the response. The test uses a short session
timeout (2 seconds) and we've seen the problem occur on CI when,
presumably, a noisy neighbour has caused some CPU starvation.

This commit increases the timeout to 5 seconds to reduce the chance of
a short period of CPU starvation causing the test to fail.

Closes gh-25572

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-session-webflux/src/test/java/smoketest/session/SampleSessionWebFluxApplicationTests.java

 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -36,7 +36,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  *
  * @author Vedran Pavic
  */
-@SpringBootTest(properties = "server.servlet.session.timeout:2",
+@SpringBootTest(properties = "server.servlet.session.timeout:5",
 		webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
 class SampleSessionWebFluxApplicationTests {
 
@@ -57,7 +57,7 @@ class SampleSessionWebFluxApplicationTests {
 		response = webClient.get().cookie("SESSION", sessionCookie.getValue()).exchange().block(Duration.ofSeconds(30));
 		assertThat(response.statusCode()).isEqualTo(HttpStatus.OK);
 		assertThat(response.bodyToMono(String.class).block(Duration.ofSeconds(30))).isEqualTo(sessionId);
-		Thread.sleep(2000);
+		Thread.sleep(5000);
 		response = webClient.get().cookie("SESSION", sessionCookie.getValue()).exchange().block(Duration.ofSeconds(30));
 		assertThat(response.statusCode()).isEqualTo(HttpStatus.UNAUTHORIZED);
 	}