releng: Promote go1.16.4/1.15.11 images

[cpanato]

What type of PR is this?

/kind feature
/area dependency release-eng/security

What this PR does / why we need it:

Tracking issue: kubernetes/release#2060

ref: kubernetes/release#2005 (comment)

• kube-cross: Build v1.16.4-1 and v1.15.12-1 images
• go-runner: Build v2.3.1-go1.16.4-buster.0 and v2.3.1-go1.15.12-buster.0
• releng-ci: Build v0.5.2 image using go1.16.4

/assign @justaugustus @saschagrunert @hasheddan
cc @kubernetes/release-engineering

[k8s-ci-robot]

@cpanato: The label(s) area/release-eng/security cannot be applied, because the repository doesn't have them.

In response to this:

What type of PR is this?

/kind feature
/area dependency release-eng/security

What this PR does / why we need it:

Tracking issue: kubernetes/release#2060

ref: kubernetes/release#2005 (comment)

• kube-cross: Build v1.16.4-1 and v1.15.12-1 images
• go-runner: Build v2.3.1-go1.16.4-buster.0 and v2.3.1-go1.15.12-buster.0
• releng-ci: Build v0.5.2 image using go1.16.4

/assign @justaugustus @saschagrunert @hasheddan
cc @kubernetes/release-engineering

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[hasheddan]

/lgtm

[ameukam]

/lgtm

[justaugustus]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cpanato, hasheddan, justaugustus

The full list of commands accepted by this bot can be found here.

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Needs approval from an approver in each of these files:

• k8s.gcr.io/images/k8s-staging-build-image/OWNERS [justaugustus]
• k8s.gcr.io/images/k8s-staging-releng/OWNERS [cpanato,hasheddan,justaugustus]

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