Bump opencv-python from 4.2.0.32 to 4.8.1.78

Bumps [opencv-python](https://github.com/opencv/opencv-python) from 4.2.0.32 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:development
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements-dev.txt

@@ -4,6 +4,6 @@ mss==4.0.3
 robotframework
 robotstatuschecker
 pillow
-opencv-python == 4.2.0.32; python_version == '2.7'
+opencv-python == 4.8.1.78; python_version == '2.7'
 opencv-python; python_version > '3.4'
 pyautogui