Use ci/latest as image for k8s_linux_apiserver

[dougsland]

Issue:

The CI Image for APIServer is static is require manually change for updating.

Steps to change it:

$ vi sync/shared/variables.yaml
k8s_linux_apiserver: "ci/v1.22.0-alpha.3.31+a3abd06ad53b2f"   <---- removed
k8s_linux_apiserver: "ci/latest"   <------ added

How to test after the change?

# git clone https://github.com/kubernetes-sigs/sig-windows-dev-tools.git
< do the changes listed above>
# sig-windows-dev-tools# make 2

Goal: make sure it's using the latest kubernetes image for CI without breaking the build process.

See discussion here for more info: https://github.com/kubernetes-sigs/sig-windows-dev-tools/pull/148

[dougsland]

/good-first-issue

[k8s-ci-robot]

@dougsland: This request has been marked as suitable for new contributors.

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[dougsland]

@knabben already fixed that using stable:

k8s_linux_apiserver="stable-${kubernetes_version}"