Use latest stable version of Xcode

Author: sbooth

.github/workflows/objective-c-xcode.yml

@@ -12,6 +12,10 @@ jobs:
     runs-on: macos-latest
 
     steps:
+    - name: Set Xcode version
+      uses: maxim-lobanov/setup-xcode@v1
+      with:
+        xcode-version: latest-stable
       - name: Checkout
         uses: actions/checkout@v4
       - name: Build for macOS