Bump opencv-python in /python/OpenVINO_EP/yolov4_object_detection (microsoft#500)

Bumps [opencv-python](https://github.com/opencv/opencv-python) from 4.5.5.64 to 4.8.1.78.
- [Release notes](https://github.com/opencv/opencv-python/releases)
- [Commits](https://github.com/opencv/opencv-python/commits)

---
updated-dependencies:
- dependency-name: opencv-python
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

python/OpenVINO_EP/yolov4_object_detection/requirements.txt

@@ -1,7 +1,7 @@
 certifi==2023.7.22
 flatbuffers==2.0
 onnx
-opencv-python==4.5.5.64
+opencv-python==4.8.1.78
 Pillow==10.3.0
 protobuf==3.20.2
 scipy==1.10.0