feat(JDK21) Use official Temurin build for linux/s390x

[gounthar]

This is a follow-up to #772.
@MarkEWaite noted that we should use the official build versions for the architectures that have moved out of preview.
@dduportal then noted that the only one that was left was s390x.

I'm proposing this small change to remove s390x's JDK from the preview and start using the official Temurin builds.

I noticed that there was no arm32 defined in check-jdk.sh, even though it is supposed to be called by the jdk21-preview manifest.

I'm not sure how we got this working for arm32 in the first place. I'm not saying it isn't working; I just don't understand how it works. 🤷

So, I haven't removed the arm32 support in this PR. I will do so in another PR, but it could have some side effects for arm32 (or not; I'm sure you all understand how this worked for arm32).

Anyway, there is no new Temurin release for arm32 in ea-beta (or anything else, to be clear), so that shouldn't be an issue.

Testing done

make build agent_debian_jdk21_preview and make build agent_debian_jdk21_preview.

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• Ensure that the pull request title represents the desired changelog entry
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[gounthar]

Somehow, the build failed, but it doesn't seem linked to the change. 🤷

https://github.com/jenkinsci/docker-agent/runs/22796738582

[dduportal]

Somehow, the build failed, but it doesn't seem linked to the change. 🤷

https://github.com/jenkinsci/docker-agent/runs/22796738582

Good catch! CI logs shows a network timeout.

But the latest agent release shows there is a JDK21 linux/s390x image 👏 : https://hub.docker.com/layers/jenkins/agent/3206.vb_15dcf73f6a_9-7-jdk21/images/sha256-e0e443a4a2501a45bf978b101aef23de781dd3b2fbb092608b4a601e0c4a2799?context=explore

[gounthar]

Good news, thanks! 👍