Update sync examples with check to async check

[inancgumus]

What?

Updates sync examples with check to async check.

Some of the examples don't require an async check, but it's better to use async check in them for consistency.

Why?

The sync k6 check is cumbersome when working with async functions.

Checklist

• I have performed a self-review of my code
• I have added tests for my changes
• I have commented on my code, particularly in hard-to-understand areas

Related PR(s)/Issue(s)

grafana/k6-docs#1725

[ankur22]

Thanks for working on this change.

My personal preference would be to avoid then chaining as i think it looks complicated to a new user who is new to JS.

I'd also only try to retrieve data to compare within a check rather than do any changes to the DOM or elsewhere in the website/system. I like to think that a check is almost like an assert, and generally we only compare two things in an assert, rather than perform state changes to the system within the assert.

Since these are both style issue though, happy to approve and get them merged in 👍

[allansson]

Thanks for doing this. 🙏

I left a few comments.

[ankur22]

Thanks! LGTM 🚀