test-infra: build-and-push-k8s-at-golang-tip broken after bootstrap update

What happened: After an update to the bootstrap image (removing python2), build-and-push-k8s-at-golang-tip sig-scalability prowjob started on a step COPY RELEASE

What you expected to happen: Removing python2 from bootstrap image does not break build-and-push-k8s-at-golang-tip prowjob

How to reproduce it (as minimally and precisely as possible): The job is on the testgrid: https://k8s-testgrid.appspot.com/sig-scalability-golang#build-and-push-k8s-at-golang-tip

Please provide links to example occurrences, if any: Same as above

Anything else we need to know?: It looks like this might be caused by an issue with gsutil after python2 is removed. Looking at the failures it seems to fail at this step: https://github.com/kubernetes/release/blob/master/push-build.sh#L947

I’ve created a PR to rollback bootstrap image for this job back (https://github.com/kubernetes/test-infra/pull/28543), but I think we should understand what is going on here.