Configure Reactor Netty quiet shutdown period in tests

See gh-24538

spring-webflux/src/test/java/org/springframework/web/reactive/function/client/WebClientDataBufferAllocatingTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -63,6 +63,7 @@ class WebClientDataBufferAllocatingTests extends AbstractDataBufferAllocatingTes
 
 	@BeforeAll
 	void setUpReactorResourceFactory() {
+		this.factory.setShutdownQuietPeriod(Duration.ofMillis(100));
 		this.factory.afterPropertiesSet();
 	}