Align with Framework's deprecation of getLastModified

See gh-27160

Author: wilkinsona

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/web/servlet/CompositeHandlerAdapter.java

@@ -61,6 +61,7 @@ public ModelAndView handle(HttpServletRequest request, HttpServletResponse respo
 	}
 
 	@Override
+	@Deprecated
 	public long getLastModified(HttpServletRequest request, Object handler) {
 		Optional<HandlerAdapter> adapter = getAdapter(handler);
 		return adapter.map((handlerAdapter) -> handlerAdapter.getLastModified(request, handler)).orElse(0L);