ci: explicitly switch macos build to silicon and upgrade xcode

[galargh]

CircleCI is removing support for Apple Intel executors on Oct 2 - see https://discuss.circleci.com/t/macos-resource-deprecation-update/46891. After that date only Apple Silicon executors will be available. This PR ensures the macos builds are executed on Apple Silicon executors only.

[vmx]

@galargh I just want to note that this repo likely isn't used anymore. I'm currently asking around if that's really the case and whether it can be archived.

[galargh]

@galargh I just want to note that this repo likely isn't used anymore. I'm currently asking around if that's really the case and whether it can be archived.

Thanks for the heads up! I'm currently trying to make it work here because there are a couple of other repos where I'll need to do similar changes so I'm using it as sort of a testing ground. Let me know if you need my help with archivisation.

[vmx]

so I'm using it as sort of a testing ground.

Better test grounds with more up to date CI might be:

• Kind of simple: https://github.com/filecoin-project/rust-filecoin-proofs-api/blob/master/.circleci/config.yml
• Go and Rust: https://github.com/filecoin-project/filecoin-ffi/blob/master/.circleci/config.yml
• Crazy: https://github.com/filecoin-project/rust-fil-proofs/blob/master/.circleci/config.yml

[galargh]

Thanks, I'm done now but I'll keep that in mind for the future 🙇

[galargh]

As per https://github.com/filecoin-project/rust-fil-proofs/pull/1722#issuecomment-1739139554, it turns out I misunderstood the announcement (timeline) slightly. I'm going to close this PR now and recreate it with correct commit messages and description. I'm sorry for the extra noise.