test: enable future java for jenkins

If the java version is to new for the lastest jenkins release it refuses
to start:

[TEST]: Waiting for Jenkins to get ready...
Running with Java 23 from /usr/lib/jvm/java-23-openjdk, which is not yet fully supported.
Run the command again with the --enable-future-java flag to enable preview support for future Java versions.
Supported Java versions are: [17, 21]
See https://jenkins.io/redirect/java-support/ for more information.

test/integration/jenkins/run.py

@@ -322,7 +322,8 @@ def download(url, dest):
             "-Djenkins.install.runSetupWizard=false",
             "-Dhudson.plugins.git.GitSCM.ALLOW_LOCAL_CHECKOUT=true",
             "-Dcasc.jenkins.config=" + os.path.abspath("jenkins.yaml"),
-            "-jar", jenkins],
+            "-jar", jenkins,
+            "--enable-future-java" ],
             env=env)
         print("[TEST]:", "Jenkins running as pid", jenkinsProc.pid, "in", jenkinsHome)