Use non-arm Mac as workaround for emulator bug

ReactiveCircus/android-emulator-runner#350

Author: nohli

.github/workflows/flutter_checks.yml

@@ -80,7 +80,7 @@ jobs:
 
   test_example:
     name: Flutter example integration test
-    runs-on: macos-latest
+    runs-on: macos-13
     timeout-minutes: 20
     steps:
       - name: Checkout repository