Switch Jenkins Core release build from jdk17 to jdk21

[Stéphane MERLE]

Hello dear Jenkins contributors,

The Jenkins infrastructure team plans to switch the Jenkins Core release to use JDK21 instead of JDK17 starting with the weekly release 2.514 that should be triggered on June 11.

The Jenkins core is already run on jdk21 as per https://github.com/jenkinsci/jenkins/blob/7732f554a6a63f18898085e4a00e8ff7769e1e09/Jenkinsfile#L17

you can follow the whole jdk21 switch here: https://github.com/jenkins-infra/helpdesk/issues/4120

and more specifically https://github.com/jenkins-infra/helpdesk/issues/4127

For the Jenkins Infra Team,

Stéphane MERLE

[Damien Duportal]

Hello folks, quick reminder that we want to have the weekly release 2.514 to be built with JDK21 (instead of JDK17) so that we have the same behavior between ci and CD (and infra can move forward on the LTS support).

Without any objections, we'll move forward to this planning (e.g. Tuesday 10 June).

For the Jenkins Infra Team,

Damien

[James Nord]

Noting this possibly caused https://github.com/jenkins-infra/helpdesk/issues/4705  I doubt there is anything that can be done about it now, but maybe something to think about for the next Java bump.