Update .ci.yaml in flutter/packages to use either macOS 15.5 or macOS 15.7.1 #176931
Description
Prerequisites
- Run all flutter/flutter macOS tests manually on macOS 15.7.1 bot #176928
- Ensure no open issues in Tracking issue for any infra or test failures with macOS 15 #167681 under flutter/packages
https://github.com/flutter/packages/blob/main/.ci.yaml
- os: Mac-14|Mac-15
+ os: Mac-15.5|Mac-15.7