git: openjdk/jdk-sandbox: json: Made clear that JsonValue is immutable

[duke]

Changeset: addb558e
Branch: json
Author:    Naoto Sato <naoto.sato at oracle.com>
Date:      2025-02-07 11:24:58 +0000
URL:       https://git.openjdk.org/jdk-sandbox/commit/addb558e8fea561fc0382706f7337178580711c7

Made clear that JsonValue is immutable

! src/java.base/share/classes/java/util/json/JsonValue.java