Set running to false when stop method is called

Update `WebServerStartStopLifecycle` to change the `running` state when
the `stop()` method is called.

Fixes gh-31966

Author: philwebb

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/servlet/context/WebServerStartStopLifecycle.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2022 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.
@@ -48,6 +48,7 @@ public void start() {
 
 	@Override
 	public void stop() {
+		this.running = false;
 		this.webServer.stop();
 	}