CircleCI: Update macos setup

[kba]

On October 2nd 2023, CircleCI will end-of-life the medium macOS resource. On this date, any jobs that run on the medium macOS resource will show an “invalid resource class” error.

You are receiving this email because you are associated with a project that has used the medium macOS resource in the last six months.

You now have access to the medium.gen2 resource with your Free plan. Our gen2 resource offers a more performant build experience with up to 50% faster macOS jobs, so you can build faster than ever before on CircleCI.

Please update the resource class key in your configuration file to macos.x86.medium.gen2 before October 2nd to enjoy faster jobs and avoid a build error. For any questions or assistance, please visit