package/opencv4: security bump to version 4.8.1
Also, bump package/opencv4-contrib to in lock-step.
This addresses both CVE-2023-2617 and CVE-2023-2618, that have been
fixed in OpenCV 4.8.0.
Signed-off-by: Woodrow Douglass <wdouglass@carnegierobotics.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>