git: openjdk/jdk-sandbox: json: Refined IAE message

[duke]

Changeset: baccb4e7
Branch: json
Author:    Naoto Sato <naoto.sato at oracle.com>
Date:      2025-05-13 15:04:38 +0000
URL:       https://git.openjdk.org/jdk-sandbox/commit/baccb4e70016343bb378262118a14613c987d35e

Refined IAE message

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