fix(updatecli): check preview parent images only for some architectures

[lemeurherve]

This PR fixes the docker-agent updatecli manifest to check the existence of preview images only for some architectures.

Follow-up of jenkinsci/docker-agent#521

Testing done

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[lemeurherve]

Output LGTM, parent image version updated: https://github.com/jenkinsci/docker-inbound-agent/actions/runs/6605870230/job/17941489762

(Not updated without this PR as the alpine21-preview image doesn't exist anymore for the amd64 & arm64 architecture, replaced by official GA Temurin JDK21 images, without "-preview" in its tag: https://github.com/jenkinsci/docker-inbound-agent/actions/runs/6605845448/job/17941442330)

[lemeurherve]

Self-merging as:

• updatecli is fixed:

  Run Summary
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  Pipeline(s) run:
    * Changed:	1
    * Failed:	0
    * Skipped:	0
    * Succeeded:	1
    * Total:	2
  

• no functional code change