Fix building with JDK 20-ea due to missing experimental flag in java17Test

hibernate-core/hibernate-core.gradle

@@ -259,6 +259,12 @@ if ( gradle.ext.javaVersions.test.release.asInt() >= 17 ) {
         useJUnitPlatform()
         testClassesDirs = sourceSets.testJava17.output.classesDirs
         classpath = sourceSets.testJava17.runtimeClasspath
+
+        if ( gradle.ext.javaVersions.test.launcher.asInt() >= 19 ) {
+            logger.warn( "The version of Java bytecode that will be tested is not supported by Bytebuddy by default. " +
+                                 " Setting 'net.bytebuddy.experimental=true'." )
+            systemProperty 'net.bytebuddy.experimental', true
+        }
     }
 
     testClasses.dependsOn compileTestJava17Java