Merge pull request #26298 from sturkmen72:avif

Proposed solution for the issue 26297 #26298

closes #26297

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/imgcodecs/test/test_avif.cpp

@@ -337,11 +337,20 @@ TEST_P(Imgcodecs_Avif_Animation_WriteDecodeSuite, encode_decode) {
   std::vector<unsigned char> buf(size);
   EXPECT_TRUE(file.read(reinterpret_cast<char*>(buf.data()), size));
   file.close();
-  EXPECT_EQ(0, remove(output.c_str()));
   std::vector<cv::Mat> anim;
   ASSERT_TRUE(cv::imdecodemulti(buf, imread_mode_, anim));
 
   ValidateRead(anim_original, anim);
+
+  if (imread_mode_ == IMREAD_UNCHANGED) {
+    ImageCollection collection(output, IMREAD_UNCHANGED);
+    anim.clear();
+    for (auto&& i : collection)
+      anim.push_back(i);
+    ValidateRead(anim_original, anim);
+  }
+
+  EXPECT_EQ(0, remove(output.c_str()));
 }
 
 INSTANTIATE_TEST_CASE_P(