Deflake ImageProvider.evict test (#35999)

packages/flutter/test/painting/image_provider_test.dart

@@ -44,11 +44,19 @@ void main() {
         final ImageCache otherCache = ImageCache();
         final Uint8List bytes = Uint8List.fromList(kTransparentImage);
         final MemoryImage imageProvider = MemoryImage(bytes);
-        otherCache.putIfAbsent(imageProvider, () => imageProvider.load(imageProvider));
+        final ImageStreamCompleter cacheStream = otherCache.putIfAbsent(
+          imageProvider, () => imageProvider.load(imageProvider),
+        );
         final ImageStream stream = imageProvider.resolve(ImageConfiguration.empty);
         final Completer<void> completer = Completer<void>();
-        stream.addListener(ImageStreamListener((ImageInfo info, bool syncCall) => completer.complete()));
-        await completer.future;
+        final Completer<void> cacheCompleter = Completer<void>();
+        stream.addListener(ImageStreamListener((ImageInfo info, bool syncCall) {
+          completer.complete();
+        }));
+        cacheStream.addListener(ImageStreamListener((ImageInfo info, bool syncCall) {
+          cacheCompleter.complete();
+        }));
+        await Future.wait(<Future<void>>[completer.future, cacheCompleter.future]);
 
         expect(otherCache.currentSize, 1);
         expect(imageCache.currentSize, 1);