docs(readme): bump action version to v5

[adriencaccia]

v5.0.0 is out, so the README GitHub Actions snippet now points at it.

Refs COD-3244 (kept open, it tracks the runner release itself)

[greptile-apps]

Greptile Summary

The README’s GitHub Actions example now references the newly released CodSpeedHQ/action@v5 instead of v4.

Confidence Score: 5/5

The documentation-only version update appears safe to merge.

The change only updates the action reference in the README example, and no concrete incompatibility or broken documentation contract is established.

Important Files Changed

Filename	Overview
README.md	Updates the documented CodSpeed GitHub Action major version from v4 to v5; no actionable issue was identified.

_{Reviews (1): Last reviewed commit: "docs(readme): bump action version to v5" | Re-trigger Greptile}

[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 17 untouched benchmarks

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_{Comparing cod-3244-bump-action-v5 (0ae10b4) with main (0418479)}