chore: update approve-to-run-ci (Meshery-Operator CI) workflow

[Katotodan]

Description
This PR update the golangci-lint job to checkout code before setting up golang.
It set the golangci/golangci-lint-action@v9 to use one of the compatible version, I have use the latest version.
The actions/checkout@master present some security vulnerability, this PR set the action to actions/checkout@v6.
It also update the actions/setup-go@v4 to actions/setup-go@v5

This PR fixes #767

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[Junnygram]

Using version: latest for golangci-lint is generally considered an anti-pattern because any new linter release can introduce new rules and unexpectedly break the CI on unrelated PRs.

In fact, this change is why the golangci-lint check is currently failing in this PR! The newer version (v2.12.2) is now flagging an unused variable here: api/v1alpha1/meshsync_types_test.go:102:4: 1 (untyped int constant) is not used (typecheck).

Could you please do two things:

1. Pin this to a specific version (e.g., version: v2.12.2) instead of using latest.
2. Fix the newly surfaced linting error in api/v1alpha1/meshsync_types_test.go so the checks can pass.