github/ci: update macOS job to macOS 15

Author: aberaud

.github/workflows/ccpp.yml

@@ -87,7 +87,7 @@ jobs:
 
   build-macos:
     name: macOS/Clang build
-    runs-on: macos-12
+    runs-on: macOS-15
     steps:
     - uses: actions/checkout@v4
     - name: Dependencies