Update k3s versions

This MR updates all existing k3s version to the latest minor release. This is important to get a bug fix for the latest kernel versions:

https://github.com/k3s-io/k3s/pull/3344 https://github.com/k3s-io/k3s/pull/3343 https://github.com/k3s-io/k3s/pull/3342

Otherwise k3s can not be started anymore on >= 5.12 -> https://github.com/rancher/k3d/issues/607

This also adds support for k3s 1.21