Merge pull request #29107 from varun-jaiswal17:yunet-dynamic-input

Update default YuNet model to new dynamic inputs #29107

Update the default model in `face_detect.py` and `face_detect.cpp` to
`face_detection_yunet_2026may.onnx`, which has symbolic `height`/`width` input dims.

## Changes
- `samples/dnn/face_detect.py`: update default `--face_detection_model` to `face_detection_yunet_2026may.onnx`
- `samples/dnn/face_detect.cpp`: update default `fd_model` to `face_detection_yunet_2026may.onnx`

Companion PR : 
- https://github.com/opencv/opencv_zoo/pull/310
- https://github.com/opencv/opencv_extra/pull/1373

 Closes : https://github.com/opencv/opencv/issues/28769
 
### 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.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/dnn/misc/python/test/test_dnn.py

@@ -286,7 +286,7 @@ class dnn_test(NewOpenCVTests):
 
 
     def test_face_detection(self):
-        model = self.find_dnn_file('dnn/onnx/models/yunet-202303.onnx', required=False)
+        model = self.find_dnn_file('dnn/onnx/models/yunet-202605.onnx', required=False)
         img = self.get_sample('gpu/lbpcascade/er.png')
 
         ref = [[1, 339.62445, 35.32416, 30.754604, 40.202126, 0.9302596],