HHH-14371 Open java.base/java.nio.charset to the unnamed module in tests

NamingHelper test needs access to Charset.defaultCharset.

Signed-off-by: Yoann Rodière <yoann@hibernate.org>

hibernate-core/hibernate-core.gradle

@@ -239,6 +239,12 @@ artifacts {
 
 test {
     systemProperty 'file.encoding', 'utf-8'
+
+    if ( gradle.ext.javaVersions.test.launcher.asInt() >= 9 ) {
+        // See org.hibernate.boot.model.naming.NamingHelperTest.DefaultCharset.set
+        jvmArgs( ['--add-opens', 'java.base/java.nio.charset=ALL-UNNAMED'] )
+    }
+
     beforeTest { descriptor ->
         //println "Starting test: " + descriptor
     }