Exclude "viewport" meta tag audit for desktop devices

**Feature request summary**
We request that Lighthouse stop auditing the "viewport" meta tag on desktop devices, as it is only relevant for mobile devices. More details: [Lighthouse Best Practices - Viewport](https://developer.chrome.com/docs/lighthouse/best-practices/viewport).

**What is the motivation or use case for changing this?**
We aim to improve our SEO Lighthouse score and believe that ignoring this audit for desktop devices would provide more accurate results.

**How is this beneficial to Lighthouse?**
This change would ensure Lighthouse properly audits the "viewport" meta tag only where it is applicable, leading to more relevant recommendations.