ci: use macos-15-intel

The macOS-13 based runner images are being deprecated, consider switching to macOS-15 (macos-15-intel) or macOS 15 arm64 (macos-latest) instead. For more details see actions/runner-images#13046

Author: inkydragon

.github/workflows/CI.yml

@@ -40,7 +40,7 @@ jobs:
           - os: macos-latest
             version: '1.0'
         include:
-          - os: macos-13  # Intel
+          - os: macos-15-intel  # Intel
             version: '1.0'
     steps:
       - uses: actions/checkout@v6