Mac CI builds are failing because the metal shader compiler cannot execute:

error: cannot execute tool 'metal' due to missing Metal Toolchain;
use: xcodebuild -downloadComponent MetalToolchain

The mac_toolchain CIPD tool detects the Metal Toolchain status as installedUpdateAvailable but treats it as "already installed" and skips the update. Xcode metal compiler requires the updated toolchain version to function.

logs:

Installing metal toolchain, if needed...
Metal toolchain already installed -- status: installedUpdateAvailable

build:
https://ci.chromium.org/ui/p/flutter/builders/try/Mac%20Engine%20Drone/2221227/overview