✨ (go/v4): enable 'import-shadowing' linter

[kersten]

Summary

This PR adds the import-shadowing linter to all .golangci.yml configuration files across test projects and templates.
The import-shadowing linter detects cases where a package import shadows an existing variable, which can lead to subtle bugs.

Motivation

Adding this linter helps maintain cleaner and more maintainable code by avoiding accidental name collisions.
This change aligns the lint configuration across the codebase and ensures new code follows the same checks.

Changes

• Added import-shadowing to:
  • testdata/project-v4*/.golangci.yml
  • test projects in docs/book/src/**/testdata
  • generated linter config in pkg/plugins/golang/v4/scaffolds/internal/templates/golangci.go

No functional code changes were made—this is purely a tooling/linting update.

[k8s-ci-robot]

Hi @kersten. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[camilamacedo86]

This one is an addition so the best, here would be ✨ ( new feature .. add a new linter )
So, I hope that you do not mind, but I have updated the title accordingly.

[camilamacedo86]

/ok-to-test
/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: camilamacedo86, kersten

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