Github Actions sunsets images based on `macOS-10.15`

[NlightNFotis]

The macOS-10.15 image in Github Actions is deprecated since May, and scheduled for deletion by 30 Aug 2022. There's also a warning to that effect in our latest release's CI run.

We need to move the jobs to macOS-11 or later by that time, or we're going to have failing jobs.

[NlightNFotis]

According to the blog post, there are more scheduled failures to raise awareness to the sunsetting of those runners, so this needs to be bumped up in priority, otherwise we're going to see intermittent failures in more of our CI runners.