Fix CI: use macos-15 runner and Xcode 16.2

Author: coenttb

.github/workflows/ci.yml

@@ -17,12 +17,12 @@ jobs:
   # Primary development workflow: Latest Swift on macOS with debug build
   macos-latest:
     name: macOS (Swift 6.2, debug)
-    runs-on: macos-26
+    runs-on: macos-15
     steps:
       - uses: actions/checkout@v5
 
       - name: Select Xcode 26.0
-        run: sudo xcode-select -s /Applications/Xcode_26.0.app
+        run: sudo xcode-select -s /Applications/Xcode_16.2.app
 
       - name: Print Swift version
         run: swift --version