fix: support legacy release downloads

[CAOShurong]

Addresses #4130

What

• route the finite set of pre-module releases to their original unprefixed tags
• install their raw executable assets instead of treating them as tar archives
• add v2.0.3 to the existing mocked-release workflow matrix

Why

install_kustomize.sh 2.0.3 currently queries kustomize/v2.0.3, even though that release is tagged v2.0.3. Its Linux asset is also a raw executable, while the current installer assumes every matching asset is a .tar.gz archive.

This follows the finite-tag approach suggested in the review of #4131 and keeps the existing module-era archive path unchanged.

Verification

• regression fixture fails before the fix when the script tries to extract the raw v2.0.3 asset
• mocked legacy, minimized, and unminimized release payloads install executable binaries
• real v2.0.3, v3.3.0, and v5.8.1 releases install and report the requested versions on Linux
• nonexistent version, missing destination, and existing destination paths still exit 1
• bash -n hack/install_kustomize.sh
• actionlint .github/workflows/test-install-kustomize.yml
• go build . and go test ./... in kustomize/ with Go 1.26.5 on Linux

make lint was attempted with the repository-pinned golangci-lint v1.64.8, but package loading timed out in the first api module under the local WSL environment. It produced no finding in the changed files; the full repository lint remains to CI.

AI assistance disclosure

OpenAI Codex assisted with issue research, implementation, and test execution. The contributor remains responsible for the submitted changes. In accordance with the Kubernetes contribution policy, review comments will be answered personally without AI assistance.

[kubernetes-prow]

This PR has multiple commits, and the default merge method is: merge.
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[linux-foundation-easycla]

• ❌ - login: @CAOShurong / name: Shurong Cao. The commit (4962003, 8853586) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please visit our EasyCLA portal and chat with our support bot.

[kubernetes-prow]

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[kubernetes-prow]

Hi @CAOShurong. Thanks for your PR.

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[kubernetes-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: CAOShurong
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[koba1t]

/ok-to-test

[koba1t]

@CAOShurong
Please pass the CLA.