Remove Mac 12 (now deprecated) from CI

Author: pimterry

.github/workflows/ci.yml

@@ -102,9 +102,6 @@ jobs:
           - platform: MacOS 13
             os: "macos-13"
             test-script: "./unix.sh darwin"
-          - platform: MacOS 12
-            os: "macos-12"
-            test-script: "./unix.sh darwin"
           - platform: Windows 2022
             os: "windows-2022"
             test-script: ".\\windows.bat"