Update Kube Versions for envtest-existing & kuttl PR Checks

[andrewlecuyer]

Updates the min/max versions of Kubernetes used by the kubernetes-k3d and kuttl-k3d PR checks. This means PR checks for envtest-existing and kuttl tests are now run against the current min/max versions of Kubernetes supported by PGO according to the Supported Platforms page in the docs.

Checklist:

• Have you added an explanation of what your changes do and why you'd like them to be included?
• Have you updated or added documentation for the change, as applicable?
• Have you tested your changes on all related environments with successful results, as applicable?
  • Have you added automated tests?

Type of Changes:

• New feature
• Bug fix
• Documentation
• Testing enhancement
• Other

What is the current behavior (link to any open issues here)?

What is the new behavior (if this is a feature change)?

• Breaking change (fix or feature that would cause existing functionality to change)

Other Information: