Use latest macos in CI

[tannewt]

No description provided.

[dhalbert]

Thanks! Despite "latest", it is really macos-15: https://github.blog/changelog/2025-07-11-upcoming-changes-to-macos-hosted-runners-macos-latest-migration-and-xcode-support-policy-updates/

[dhalbert]

ehh:

fatal error: /Applications/Xcode_16.4.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/lipo: mpy-cross/build/mpy-cross and mpy-cross/build-arm64/mpy-cross-arm64 have the same architectures (arm64) and can't be in the same fat output file

[dhalbert]

ehh

fatal error: /Applications/Xcode_16.4.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/lipo: mpy-cross/build/mpy-cross and mpy-cross/build-arm64/mpy-cross-arm64 have the same architectures (arm64) and can't be in the same fat output file

Intel macos is only supported for free runners on macos-13. So I think we need to punt on Intel macos mpy-cross now.
See actions/runner-images#10810

build failure

[dhalbert]

With this PR, we are no longer building Intel or universal macOS mpy-cross now. mpy-cross is being built with macos-latest, which is macOS 15. But without paying, we can no longer build on macos-15 on an Intel platform.

[dhalbert]

It looks like GitHub changed their mind, and macos-15-intel is available: actions/runner-images#13045. We could add it back, or just wait and see if anyone has an issue with no more Intel mpy-cross binaries available.