Clean up warnings in Gradle build

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestResponseBodyMethodProcessorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -839,12 +839,12 @@ class RequestResponseBodyMethodProcessorTests {
 	}
 
 
+	@SuppressWarnings("serial")
 	private static class MyProblemDetail extends ProblemDetail {
 
 		public MyProblemDetail(HttpStatus status) {
 			super(status.value());
 		}
-
 	}