fix CI: run tests only on macOS due to plutil dependency

- Changed CI to run on macos-latest instead of Linux/Windows
- Tests require plutil command which is macOS-specific
- Removed matrix strategy since only one OS is needed
- Fixes 'spawn plutil ENOENT' error on non-macOS runners

Author: EvanBacon

.github/workflows/ci.yml

@@ -8,11 +8,7 @@ on:
 
 jobs:
   test:
-    runs-on: ${{ matrix.os }}
-    
-    strategy:
-      matrix:
-        os: [ubuntu-latest, windows-latest]
+    runs-on: macos-latest
 
     steps:
     - name: Checkout code