Test Apple CI against GitHub's Xcode 27 runner image

GitHub has added a public-preview Xcode 27 runner image for GitHub-hosted macOS runners. Use it when you need early CI coverage for Apple SDK and Xcode compatibility before the toolchain becomes the default in your release workflow.

What to check:

• Update runs-on only in a test branch or canary workflow first.
• Confirm the supported runner label from GitHub's changelog before changing production workflows.
• Expect arm64 macOS support only; Intel runners are not included for this image.
• Compare installed software versions against your current macOS image before treating failures as app regressions.
• Keep pinned production workflows stable until signing, simulator, dependency cache, and build-time differences are understood.

This is a practical CI validation resource, not a broad platform-news story. It is useful for iOS, macOS, watchOS, and visionOS teams that want earlier warning on Xcode 27 build or test failures.