Change and fix property visibility in lazy-objects example #3 (#4294)

With private visibility on id property for class BlogPost, example 3 is not functional. Changing visibility to public resolves this error. All properties are set to public in this example for homogeneity.

language/oop5/lazy-objects.xml

@@ -141,9 +141,9 @@ int(1)
 class BlogPost
 {
     public function __construct(
-        private int $id,
-        private string $title,
-        private string $content,
+        public int $id,
+        public string $title,
+        public string $content,
     ) { }
 }