Fix bug in compatibility version script: kubelet not upgraded

[Jefftree]

Noticed a warning message in the upgrade script:

docker: 'docker cp' requires 2 arguments

Usage:  docker cp [OPTIONS] CONTAINER:SRC_PATH DEST_PATH|-
	docker cp [OPTIONS] SRC_PATH|- CONTAINER:DEST_PATH

Run 'docker cp --help' for more information

On further inspection, find returns two variables that get passed to docker cp which causes an error.

jying@jefftree ~/w/k/kubernetes ❯❯❯ find ./_output/ -type f -name kubelet                                                             
./_output/dockerized/bin/linux/amd64/kubelet
./_output/dockerized/go/bin/kubelet

Even in the logs of successful runs (https://storage.googleapis.com/kubernetes-ci-logs/logs/ci-kubernetes-e2e-kind-two-steps-upgrade-n-minus-1/1991867497766195200/build-log.txt), "Updated kubelet" never appears in the logs.

This addresses an orthogonal issue that isn't directly tied to the flake

/hold

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This pull-request has been approved by: Jefftree, siyuanfoundation

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