ci: use macos-15 for all testing to use Xcode 16.2

Author: scenee

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
         include:
           - swift: "5"
             xcode: "16.2"
-            runs-on: macos-14
+            runs-on: macos-15
           - swift: "5.10"
             xcode: "15.4"
             runs-on: macos-14
@@ -92,7 +92,7 @@ jobs:
           -sdk iphonesimulator
 
   swiftpm:
-    runs-on: macos-14
+    runs-on: macos-15
     env:
       DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
     strategy: