Update k8s.gcr.io/kube-apiserver Docker tag to v1.21.12

This MR contains the following updates:

Package	Type	Update	Change
k8s.gcr.io/kube-apiserver	ironbank-docker	patch	v1.21.11 -> v1.21.12
k8s.gcr.io/kube-apiserver		patch	v1.21.11 -> v1.21.12
k8s.gcr.io/kube-apiserver	stage	patch	v1.21.11 -> v1.21.12

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