UniqueSecurityAnnotationScanner should consider annotation on target class level as fallback

public abstract class AbstractController {

	@GetMapping("/get")
	public String get() {
		return "OK";
	}

}

@RestController
@Secured("USER")
public class DemoController extends AbstractController {

	/*
	public String get() {
		return super.get();
	}
	*/
}

demoController.get() is not protected by @Secured("USER"), we have to redefine it again.

I tried to fix it by adding

		annotations = findClosestClassAnnotations(targetClass, new HashSet<>());
		if (!annotations.isEmpty()) {
			return annotations;
		}

after
https://github.com/spring-projects/spring-security/blob/b9f3a28678af525e70cd5aa00abc816163cdb4fe/core/src/main/java/org/springframework/security/core/annotation/UniqueSecurityAnnotationScanner.java#L159-L162
but it broken GH-15352.

Start in core/src/main/java/org/springframework/security/core/annotation/UniqueSecurityAnnotationScanner.java around lines 159-162 and trace how annotations are resolved for the target class. Reproduce the AbstractController/DemoController case, then verify that class-level fallback protection works without regressing GH-15352.