Bump opencv-python from 4.8.0.76 to 4.8.1.78 in /docs (#434)

Bumps [opencv-python](https://github.com/opencv/opencv-python) from 4.8.0.76 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
  update-type: version-update:semver-patch
...

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

docs/requirements.txt

@@ -3,5 +3,5 @@ sphinx==7.2.6
 sphinx-click==5.0.1
 myst_parser==2.0.0
 ghostscript==0.7
-opencv-python==4.8.0.76
+opencv-python==4.8.1.78
 matplotlib==3.8.0