Fix ScheduledTasksEndpointAutoConfigurationTests

Update the `CustomEndpointConfiguration` class in
`ScheduledTasksEndpointAutoConfigurationTests` to be package private
so that it can be enhanced by cglib.

Prior to merge commit 361437f the class was a lite configuration so
it didn't matter that it was a private class.

Author: philwebb

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/scheduling/ScheduledTasksEndpointAutoConfigurationTests.java

@@ -62,7 +62,7 @@ public void endpointBacksOffWhenUserProvidedEndpointIsPresent() {
 	}
 
 	@Configuration
-	private static class CustomEndpointConfiguration {
+	static class CustomEndpointConfiguration {
 
 		@Bean
 		public CustomEndpoint customEndpoint() {