Bump Kubernetes dependency

[glyn]

#73 forked some code from Kubernetes in order to pick up kubernetes/kubernetes#89060 as a fix, or at least a workaround, for kubernetes/kubernetes#89016. Once this PR has landed or the issue has been solved some other way, sheaf should rebase on the Kubernetes code.

Affected files:

• third_party/github.com/kubernetes/kubernetes/staging/src/k8s.io/apimachinery/pkg/util/yaml/decoder.go
• third_party/github.com/kubernetes/kubernetes/staging/src/k8s.io/apimachinery/pkg/util/yaml/decoder_test.go

which were forked from staging/src/k8s.io/apimachinery/pkg/util/yaml in https://github.com/kubernetes/kubernetes.