Fix spelling error for cv2.aruco.DICT from 6x6_50 to 7x7_1000

[VishalBalaji321]

Hi,

There was mismatch of capitalisation of "X" for OpenCV cv2.aruco.DICT_nXn_ in camera_calibration package for dicts 6x6_50 to 7x7_1000

Previously:

"6x6_50"    : cv2.aruco.DICT_6x6_50,
"6x6_100"    : cv2.aruco.DICT_6x6_100,
"6x6_250"    : cv2.aruco.DICT_6x6_250,
...

After

"6x6_50"    : cv2.aruco.DICT_6X6_50,
"6x6_100"    : cv2.aruco.DICT_6X6_100,
"6x6_250"    : cv2.aruco.DICT_6X6_250,
...

This error came into notice when using charuco markers for calibration

[mikeferguson]

Confirmed that cv2.aruco does in fact use uppercase X for all of these

[mikeferguson]

CI appears to be broken after rolling to 24.04 migration - I don't see any formatting issues here, so merging