Use macos-15 not macos-latest if it works any better?

Author: juri

.github/workflows/build.yml

@@ -9,7 +9,7 @@ on:
 
 jobs:
   build:
-    runs-on: macos-latest
+    runs-on: macos-15
 
     steps:
       # setup-swift doesn't support Swift 6 so use the Swift included in macos-latest.