Ignore labels doesnot work as expected

[Inshu0302]

Checklist

• I have searched for similar issues.
• I have tested with the latest development wheel.
• I have checked the release documentation and the latest documentation (for main branch).

Describe the issue

I have been trying to train my custom dataset using Randlanet, Kpconv and point transformer, when I use ignore classes in configs the classes are still being used for training as well as loss calculation.

Steps to reproduce the bug

Should I share my dataset py file here to see if there is an issue within it.

Error message

No response

Expected behavior

No response

Open3D, Python and System information

- Operating system: (e.g. OSX 10.15, Ubuntu 18.04, Windows 10 64-bit)
- Python version: (e.g. Python 3.8 / output from `import sys  print(sys.version)`)
- Open3D version: (output from python: `print(open3d.__version__)`)
- System type: (x84 / arm64 / apple-silicon / jetson / rpi)
- Is this remote workstation?: yes or no
- How did you install Open3D?: (e.g. pip, conda, build from source)
- Compiler version (if built from source): (e.g. gcc 7.5, clang 7.0)

Additional information

No response