Include Windows builds of cmd/nop in release process

[imjasonh]

Fixes #4471

Changes

This uses the same multi-platform-and-multi-OS base image used for the entrypoint image to ensure that the nop image used for Affinity Assistant, etc., is also built for Windows.

/kind feature

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

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Release Notes

Include Windows support for the nop image, to enable Affinity Assistant for Windows, and more.

[imjasonh]

cc @lippertmarkus

[imjasonh]

/test tekton-pipeline-unit-tests

[imjasonh]

/test pull-tekton-pipeline-alpha-integration-tests

[ghost]

/lgtm

[tekton-robot]

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