Make nested classes in JsonTestersAutoConfiguration package private

Closes gh-15444

spring-boot-project/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/json/JsonTestersAutoConfiguration.java

@@ -118,7 +118,7 @@ public class JsonTestersAutoConfiguration {
 	/**
 	 * {@link FactoryBean} used to create JSON Tester instances.
 	 */
-	private static class JsonTesterFactoryBean<T, M> implements FactoryBean<T> {
+	static class JsonTesterFactoryBean<T, M> implements FactoryBean<T> {
 
 		private final Class<?> objectType;
 
@@ -166,7 +166,7 @@ public class JsonTestersAutoConfiguration {
 	/**
 	 * {@link BeanPostProcessor} used to initialize JSON testers.
 	 */
-	private static class JsonMarshalTestersBeanPostProcessor
+	static class JsonMarshalTestersBeanPostProcessor
 			extends InstantiationAwareBeanPostProcessorAdapter {
 
 		@Override