Update .ci.yaml in flutter/flutter to use Xcode 26 and macOS 15 #172858
Description
Prerequisites
- Run all flutter/flutter macOS tests using Xcode 26 and iOS 26 simulator #172855
- Upgrade remaining devicelab bots in each pool to macOS 15.5+ #167840
- Upgrade remaining chromium bots in each pool to macOS 15.5 #167841
- Ensure no open issues in ☂️ Tracking issue for any infra or test failures with Xcode 26 and iOS 26 Simulators #172857 under flutter/flutter
Instructions
TODO