ci: bump actions/checkout to v5 (Node 24 runtime)

Resolves the Node.js 20 deprecation warning — checkout@v5 runs natively on
Node 24, so no FORCE_JAVASCRIPT_ACTIONS_TO_NODE24 flag is needed.

Author: fexxdev

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
   test:
     runs-on: macos-15
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
 
       - name: Show Xcode version
         run: xcodebuild -version