Bump opencv-python from 4.7.0.68 to 4.8.1.78

Bumps [opencv-python](https://github.com/opencv/opencv-python) from 4.7.0.68 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] <[email protected]>