CEL: Need Test Coverage against Multiple Kubernetes Versions

[robscott]

What happened:
In #3205 we were fortunate to be running an old version of Kubernetes that caught a CEL cost estimation error described in kubernetes/kubernetes#126239. Since we claim support for 5 trailing versions of Kubernetes, we need to have test coverage that ensures our CRDs are valid across that range, at minimum testing the newest and oldest version in that range.

What you expected to happen:
Have proper test coverage across the Kubernetes versions we support.

Anything else we need to know?:
@howardjohn is working on istio/api#3275 for Istio, we likely want to copy that pattern for Gateway API. Alternatively we could use different versions of https://github.com/kubernetes-sigs/kubectl-validate, or continue spinning up kind clusters and just have different CI jobs for different k8s versions.