Added missing Javadocs for Java 21

src/main/java/org/json/JSONPropertyName.java

@@ -21,6 +21,7 @@ import java.lang.annotation.Target;
 @Target({METHOD})
 public @interface JSONPropertyName {
     /**
+     * The value of the JSON property.
      * @return The name of the property as to be used in the JSON Object.
      */
     String value();