Prerequisites

• Upgrade 50% of devicelab bots in each pool to macOS 15.7.1 #176932
• Upgrade 50% of chromium bots to macOS 15.7.1 #176933
• CP macOS 15.7.1 fixes for beta and stable #176941 - may want to wait for one release to be successful with those changes before doing this

CP the following to beta and stable:

• Update .ci.yaml in flutter/flutter to use either macOS 15.5 or macOS 15.7 #176930