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

[grant-he]

Additionally, fix bug to properly identify dynamically created group snapshots for fixed group snapshot content names when group snapshots are being deleted.

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-snapshotter repo so various Go linters
no longer raise any warnings for the code. The repo should follow modern Go constructs and best practices.
Secondly, this PR fixes an edge case bug where volumegroupsnapshot deletion fails handling dynamically created
volumegroupsnapshots.

Which issue(s) this PR fixes:

Fixes #

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

Does this PR introduce a user-facing change?: yes

Fix: edge case where volumegroupsnapshot deletion fails handling dynamically created volumegroupsnapshots.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[k8s-ci-robot]

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/lifecycle stale

[k8s-triage-robot]

The Kubernetes project currently lacks enough active contributors to adequately respond to all PRs.

This bot triages PRs according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
• After 30d of inactivity since lifecycle/stale was applied, lifecycle/rotten is applied
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/lifecycle rotten