Unpin k8s.io/kubernetes dependency from 1.19

[nikimanoledaki]

Description

Closes https://github.com/weaveworks/eksctl-ci/issues/51 Integration Test: https://github.com/weaveworks/eksctl-ci/runs/7782986905?check_suite_focus=true

We were pinning k8s to 1.19, but EKS stopped supporting 1.19 on 1 August, which is when the integration tests started failing.

Checklist

• [ ] Added tests that cover your change (if possible)
• [ ] Added/modified documentation as required (such as the README.md, or the userdocs directory)
• [ ] Manually tested
• [ ] Made sure the title of the PR is a good description that can go into the release notes
• [x] (Core team) Added labels for change area (e.g. area/nodegroup) and kind (e.g. kind/improvement)

BONUS POINTS checklist: complete for good vibes and maybe prizes?! :exploding_head:

• [ ] Backfilled missing tests for code in same general area :tada:
• [ ] Refactored something and made the world a better place :star2:

[nikimanoledaki]

The windows suite failed with the same error as the one on main, which seems like a separate problem.