Switch to macos-14, since 12 is no longer supported

Author: hosaka

.github/workflows/main.yml

@@ -28,7 +28,7 @@ jobs:
           - os: Windows
             image: windows-2022
           - os: MacOS
-            image: macos-12
+            image: macos-14
       fail-fast: false
     defaults:
       run: