Update Jenkinsfile to use JDK 21 for JBang tests

[apupier]

Description

given that there is now an enforcer to compile with JDK 21 by default. I propose this first iteration to jhave green build back.

ideally, we should compile with JDK 21 and tests with JDK 17, 21 and 25.
A good intermediate step which shoudl be enough would be to create a matrix jobs whcih is compiling and testing with JDK 17, 21 and 25 with the JDk 17 one skipping the enforcer java rule.

Note that I also removed the branches from the triggeres as there are specific jobs for that

Target

• I checked that the commit is targeting the correct branch (Camel 4 uses the main branch)

Tracking

• If this is a large change, bug fix, or code improvement, I checked there is a JIRA issue filed for the change (usually before you start working on it).

Apache Camel coding standards and style

• I checked that each commit in the pull request has a meaningful subject line and body.

• I have run mvn clean install -DskipTests locally from root folder and I have committed all auto-generated changes.

[github-actions]

🌟 Thank you for your contribution to the Apache Camel project! 🌟
🤖 CI automation will test this PR automatically.

🐫 Apache Camel Committers, please review the following items:

• First-time contributors require MANUAL approval for the GitHub Actions to run
• You can use the command /component-test (camel-)component-name1 (camel-)component-name2.. to request a test from the test bot although they are normally detected and executed by CI.
• You can label PRs using skip-tests and test-dependents to fine-tune the checks executed by this PR.
• Build and test logs are available in the summary page. Only Apache Camel committers have access to the summary.

⚠️ Be careful when sharing logs. Review their contents before sharing them publicly.

[apupier]

I modified the script on Jenkins on this build https://ci-builds.apache.org/job/Camel/job/Camel%20Jbang%20IT%20Tests/job/main/435/cloudbees-pipeline-explorer/

we can notice that it goes further (even if failing)