Update GitHub Actions to Use Latest Stable Versions and Improve Coverage Workflow

[DeRuina]

• Updated workflow to use actions/checkout@v4 and actions/setup-go@v5 for better support and long-term maintenance.
• Changed Go version setting to 'stable' to automatically track the latest stable release.
• Ensured correct order of steps: checkout runs before setup-go.

This change improves CI stability, aligns with best practices, and future-proofs the Go setup.

[DeRuina]

@mattn The Go team no longer maintains 1.13 — support for it ended in 2021(That's why the workflow failed).
I've updated the workflow to use Go 1.16 as the minimum version, which is the earliest version reliably supported across all platforms in the matrix (including modern Macs with Apple Silicon).