fix the version of opencv-python
According to the [upstream issue](https://github.com/opencv/opencv-python/issues/885), opencv-python has some compatibility problem with numpy. Since we fixed the numpy version in the requirements.txt, we also need to fix the opencv-python's verison too. I install the nightly Torch and TorchBench, there is an installation error same with the above issue. opencv-python 4.7.0.72 works well. I think we'd better fix its version until the latest opencv-python 4.9.0 released.
