fix flaky story image cache test

Author: knotbin

test/src/features/stories/ui/pages/story_page_test.dart

@@ -152,7 +152,7 @@ Future<void> _cacheImage(String url) async {
   PaintingBinding.instance.imageCache.putIfAbsent(
     key,
     () => OneFrameImageStreamCompleter(
-      Future.value(ImageInfo(image: frame.image)),
+      Future.value(ImageInfo(image: frame.image.clone())),
     ),
   );
   addTearDown(() {