Update Github CI versions.

- Use latest macOS and default Xcode versions for primary CI environment.
- Github CI no longer supports macOS 11.
  Update legacy CI to macOS 12 and Xcode 13.4.1.

.github/workflows/CI.yml

@@ -15,16 +15,17 @@ jobs:
  build:
  strategy:
  matrix:
- xcode: [ "15.0" ]
+ # Primary build on latest macOS and its default Xcode version
+ os: [ "macos-latest" ]
+ xcode: "latest"
  platform: [ "all", "macos", "ios" ]
- os: [ "macos-13" ]
  upload_artifacts: [ true ]
 
- # Legacy configurations
+ # Legacy build. Up to 3 versions behind latest (or beta).
  include:
- - xcode: "12.5.1"
+ - os: "macos-12"
+ xcode: "13.4.1"
  platform: "macos"
- os: "macos-11"
  upload_artifacts: false
  fail-fast: false