Update digitalocean_kubernetes_cluster.cloud_runner.version

The validate-plan-{production,staging} jobs started failing today with the following message:

Error: Missing required argument

with module.do.digitalocean_kubernetes_cluster.cloud_runner, on digitalocean/resources.tf line 19, in resource "digitalocean_kubernetes_cluster" "cloud_runner": 19: version = data.digitalocean_kubernetes_versions.versions.latest_version

The argument "version" is required, but no definition was found. (xref https://gitlab.wikimedia.org/repos/releng/gitlab-cloud-runner/-/jobs/128985)

Try to resolve this build problem by replacing "versions" with "example" in the middle of the data accessor to correspond to the directions at https://docs.digitalocean.com/reference/terraform/reference/resources/kubernetes_cluster/#auto-upgrade-example