Address various linter (staticcheck, modernize, etc.) comments.

[grant-he]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change
/kind bug

/kind cleanup

/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it: this PR seeks to update the external-resizer repo so various Go linters no longer
raise any warnings for the code. The repo should follow modern Go constructs and best practices.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer: I am happy to explain any part of my change.

Does this PR introduce a user-facing change?: no

NONE

[k8s-ci-robot]

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[k8s-ci-robot]

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[k8s-ci-robot]

Hi @grant-he. Thanks for your PR.

I'm waiting for a kubernetes-csi 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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[k8s-ci-robot]

PR needs rebase.

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