Make class package-private as it's returned from package-private method

Returning a private class from a package-private method causes the
AOT-generated source files to fail to compile as the private class is
not visible.

Closes gh-33106

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/endpoint/web/reactive/WebFluxEndpointManagementContextConfiguration.java

@@ -142,7 +142,7 @@ static ServerCodecConfigurerEndpointObjectMapperBeanPostProcessor serverCodecCon
 	 * {@link BeanPostProcessor} to apply {@link EndpointObjectMapper} for
 	 * {@link OperationResponseBody} to {@link Jackson2JsonEncoder} instances.
 	 */
-	private static class ServerCodecConfigurerEndpointObjectMapperBeanPostProcessor implements BeanPostProcessor {
+	static class ServerCodecConfigurerEndpointObjectMapperBeanPostProcessor implements BeanPostProcessor {
 
 		private static final List<MediaType> MEDIA_TYPES = Collections
 				.unmodifiableList(Arrays.asList(MediaType.APPLICATION_JSON, new MediaType("application", "*+json")));