Declare webSocketRegistryListener() as static method

Closes gh-3077

spring-session-core/src/main/java/org/springframework/session/web/socket/config/annotation/AbstractSessionWebSocketMessageBrokerConfigurer.java

@@ -112,7 +112,7 @@ public void configureWebSocketTransport(WebSocketTransportRegistration registrat
 	}
 
 	@Bean
-	public WebSocketRegistryListener webSocketRegistryListener() {
+	public static WebSocketRegistryListener webSocketRegistryListener() {
 		return new WebSocketRegistryListener();
 	}