Restore the WidgetTester's original surface size after testing setSurfaceSize (#87202)

Fixes https://github.com/flutter/flutter/issues/87194

packages/flutter_test/test/widget_tester_live_device_test.dart

@@ -82,7 +82,9 @@ No widgets found at Offset(1.0, 1.0).
       ),
     );
 
+    final Size originalSize = tester.binding.createViewConfiguration().size;
     await tester.binding.setSurfaceSize(const Size(2000, 1800));
+    try {
       await tester.pump();
 
       final Offset widgetCenter = tester.getRect(find.byType(Text)).center;
@@ -107,6 +109,9 @@ Some possible finders for the widgets at Offset(1000.0, 900.0):
       expect(printedMessages, equals('''
 No widgets found at Offset(1.0, 1.0).
 '''.trim().split('\n')));
+    } finally {
+      await tester.binding.setSurfaceSize(originalSize);
+    }
   });
 }