Increase github actions concurrent job limits 20->60

Is your feature request related to a problem? Please describe. We are having more and more CI jobs these days, and they're being slowed down noticably by the concurrent job limit. See for example this run, which should be pretty average. It took 20 minutes to complete, even though the longest individual job only took half that time (windows tests). This is a significant slowdown for our developers on one platform trying to make their code work with another platform.

A maintainer should probably reach out to github and request a higher limit. According to this document,

You may be rate limited by GitHub Actions when you scale your usage. Some limits can be increased by contacting us through the GitHub Support portal.

I'm not entirely sure if this is referring to maxing out your monthly minutes usage or something else. But its worth a try.

I also think that we would be able to properly justify the increase. Wgpu is a large open source project, and because it uses GPUs, it necessarily has extensive testing on each OS/CPU, which works out to many jobs.