Merge pull request #28127 from StefaniaHergane:hs/deprecated_ov_element_undefined

Update deprecated ov::element::undefined #28127

### Summary
Fixing OpenCV build error below.
Relates to OpenVINO 2026.0 updates on `ov::element::undefined` (https://github.com/openvinotoolkit/openvino/pull/32573) - replaced by `ov::element::dynamic`.
```
/home/jenkins/agent/workspace/openVINO-builder/opencv_source/opencv-opencv-f627368/modules/gapi/src/backends/ov/govbackend.cpp
[2025-12-03T21:25:54.540Z] /home/jenkins/agent/workspace/openVINO-builder/opencv_source/opencv-opencv-f627368/modules/gapi/src/backends/ov/govbackend.cpp: In function ���ov::element::Type toOV(int)���:
[2025-12-03T21:25:54.540Z] /home/jenkins/agent/workspace/openVINO-builder/opencv_source/opencv-opencv-f627368/modules/gapi/src/backends/ov/govbackend.cpp:114:25: error: ���undefined��� is not a member of ���ov::element���
[2025-12-03T21:25:54.540Z]   114 |     return ov::element::undefined;
...
/home/jenkins/agent/workspace/openVINO-builder/opencv_source/opencv-opencv-f627368/modules/gapi/test/infer/gapi_infer_ov_tests.cpp
[2025-12-03T21:26:19.642Z] /home/jenkins/agent/workspace/openVINO-builder/opencv_source/opencv-opencv-f627368/modules/gapi/test/infer/gapi_infer_ov_tests.cpp: In function ���ov::element::Type opencv_test::toOV(int)���:
[2025-12-03T21:26:19.642Z] /home/jenkins/agent/workspace/openVINO-builder/opencv_source/opencv-opencv-f627368/modules/gapi/test/infer/gapi_infer_ov_tests.cpp:832:25: error: ���undefined��� is not a member of ���ov::element���
[2025-12-03T21:26:19.642Z]   832 |     return ov::element::undefined;
```

### 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
- [ ] The PR is proposed to the proper branch
- [ ] There is a reference to the original bug report and related work
- [ ] 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/gapi/src/backends/ov/govbackend.cpp

@@ -111,7 +111,7 @@ static ov::element::Type toOV(int depth) {
         case CV_16F: return ov::element::f16;
         default: GAPI_Error("OV Backend: Unsupported data type");
     }
-    return ov::element::undefined;
+    return ov::element::dynamic;
 }
 
 static ov::preprocess::ResizeAlgorithm toOVInterp(int interpolation) {

modules/gapi/test/infer/gapi_infer_ov_tests.cpp

@@ -829,7 +829,7 @@ static ov::element::Type toOV(int depth) {
     case CV_16F: return ov::element::f16;
     default: GAPI_Error("OV Backend: Unsupported data type");
     }
-    return ov::element::undefined;
+    return ov::element::dynamic;
 }
 
 struct TestMeanScaleOV : public ::testing::TestWithParam<int>{