Bugs in Pascal Context GT visualization

[LWShowTime]

Instructions To Reproduce the 🐛 Bug:

1. Full runnable code or full changes you made:

details can refer to the failed pull requests: #5391

2. What exact command you run:
   I run the tools/visualize_data and find the visualize.py in utils have an out of date numpy dtype.

3. Full logs or other relevant observations:

this should be train(id:359) howver is overflow and refer to fly(id:359-256=103)

5. please simplify the steps as much as possible so they do not require additional resources to
   run, such as a private dataset.

expect to handle classes more than 256, however Pascal Context 459 is overflow.

Environment:

Python 3.10 numpy 1.22.4 torch 1.13.1