Return MacOS tests back into CI

[olegbespalov]

What?

In #3528, we enabled the MacOS tests. Unfortunately, the performance of MacOS seems to have caused us a lot of failures, especially considering that we know some of our tests are flaky.

In #3695, we temporarily disabled the Mac OS platform again, but we should figure out and re-enable the tests again once that is possible.

Examples of failures

https://github.com/grafana/k6/pull/3695#issuecomment-2066565482

TBD

Why?

Testing on all popular platforms is an essential part of the development process.