Update source code url for docker-inbound-agent

[liangxia]

Testing done

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Repo https://github.com/jenkinsci/docker-inbound-agent has been archived on Jan 22, 2024. Its content is now included in https://github.com/jenkinsci/docker-agent/.

[Vlatombe]

Thanks!