We use macos-14 images for macos-aarch64 runners. We use Xcode 14.3.1 there. Xcode 14 goes away from those runners, as per: https://github.com/actions/runner-images/issues/10703. Current GH runner docs say macos-14 image defaults to Xcode 15.4: https://github.com/actions/runner-images/blob/main/images/macos/macos-14-Readme.md. We can switch to that.

I think this policy change is why we started seeing GHA failures like:

```
Run # On macOS we need to install some dependencies for testing
==> Downloading https://ghcr.io/v2/homebrew/core/make/manifests/4.4.1-1
==> Fetching make
==> Downloading https://ghcr.io/v2/homebrew/core/make/blobs/sha256:94377dc5a364da305c75fd7aa923a42897993de9edd1eb074428e13c3f2aaf93
==> Pouring make--4.4.1.arm64_sonoma.bottle.1.tar.gz
==> Caveats
GNU "make" has been installed as "gmake".
If you need to use it as "make", you can add a "gnubin" directory
to your PATH from your bashrc like:

    PATH="/opt/homebrew/opt/make/libexec/gnubin:$PATH"
==> Summary
🍺 /opt/homebrew/Cellar/make/4.4.1: 17 files, 1.3MB
xcode-select: error: invalid developer directory '/Applications/Xcode_14.3.1.app/Contents/Developer'
Error: Process completed with exit code 1.
```