docker: upgrade to golang 1.21 and alpine 3.18

[mcluseau]

Upgrade versions used in the docker, and also upgrade Ginkgo so it's the same as the CLI, allowing the tests to run.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mcluseau

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/kubernetes-sigs/kpng/blob/master/OWNERS)~~ [mcluseau] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[mcluseau]

@jayunit100 is it lgtm for you? :)

[qabpea]

/lgtm

[jayunit100]

Ah thxxxx