[path_provider] Skip verifying sample file on macOS (flutter#6874)

[Sandboxing was recently disabled for macOS CI tests](flutter#149618). This caused `getApplicationDocumentsDirectory` tests in path_provider to fail because it changes the path.

With sandboxing enabled, the path is `~/Library/Containers/dev.flutter.plugins.pathProviderExample/Data/Documents`. With sandboxing disabled, the path is `~/Documents`, which requires additional permissions to access. 

To workaround, skip verifying a file can be created/deleted and simply validate a path is returned.

Fixes flutter#149713.

Author: vashworth

packages/path_provider/path_provider/example/integration_test/path_provider_test.dart

@@ -17,7 +17,15 @@ void main() {
 
   testWidgets('getApplicationDocumentsDirectory', (WidgetTester tester) async {
     final Directory result = await getApplicationDocumentsDirectory();
-    _verifySampleFile(result, 'applicationDocuments');
+    if (Platform.isMacOS) {
+      // _verifySampleFile causes hangs in driver when sandboxing is disabled
+      // because the path changes from an app specific directory to
+      // ~/Documents, which requires additional permissions to access on macOS.
+      // Instead, validate that a non-empty path was returned.
+      expect(result.path, isNotEmpty);
+    } else {
+      _verifySampleFile(result, 'applicationDocuments');
+    }
   });
 
   testWidgets('getApplicationSupportDirectory', (WidgetTester tester) async {

packages/path_provider/path_provider_foundation/example/integration_test/path_provider_test.dart

@@ -20,7 +20,15 @@ void main() {
   testWidgets('getApplicationDocumentsDirectory', (WidgetTester tester) async {
     final PathProviderPlatform provider = PathProviderPlatform.instance;
     final String? result = await provider.getApplicationDocumentsPath();
-    _verifySampleFile(result, 'applicationDocuments');
+    if (Platform.isMacOS) {
+      // _verifySampleFile causes hangs in driver when sandboxing is disabled
+      // because the path changes from an app specific directory to
+      // ~/Documents, which requires additional permissions to access on macOS.
+      // Instead, validate that a non-empty path was returned.
+      expect(result, isNotEmpty);
+    } else {
+      _verifySampleFile(result, 'applicationDocuments');
+    }
   });
 
   testWidgets('getApplicationSupportDirectory', (WidgetTester tester) async {