[BUG] Trying to train a model for classification gives a weird warning

[sarthakpati]

Describe the bug

When trying to train any classification model (and this is most prevalent for binary classification), the following UserWarning from sklearn pops up at every step per subject: y_pred contains classes not in y_true.

To Reproduce

Steps to reproduce the behavior:

1. Use any data for binary classification (TIL, EGFR, ...).
2. Try to train.
3. See the following warnings:

   
   The ``converters`` are currently experimental. It may not support operations including (but not limited to) Functions in ``torch.nn.functional`` that involved data dimension

[SNIP!]

---

Starting validation :

---

C:\Projects\GaNDLF\venv\Lib\site-packages\sklearn\metrics_classification.py:2399: UserWarning: y_pred contains classes not in y_true warnings.warn("y_pred contains classes not in y_true")

The first warning comes from [this line](https://github.com/M3DV/ACSConv/blob/95dc860a77e309f010a3d8be1f675e77c7dfeda4/acsconv/converters/__init__.py#L6).

### Expected behavior
This warning should come up just once.

### Media
N.A.

### Environment information
<!-- Put the output of the following command:
python ./gandlf_debugInfo
-->
```powershell
GANDLF version: 0.0.20-dev
Git hash: 000ea17ecd2e018dafa2ecfe7a85c030bb4a02cb
Platform: Windows-10-10.0.22631-SP0
Machine: AMD64
Processor: Intel64 Family 6 Model 165 Stepping 2, GenuineIntel
Architecture: 64bit WindowsPE
Python environment:
  Version: 3.11.6
  Implementation: CPython
  Compiler: MSC v.1935 64 bit (AMD64)
  Build: main Oct  3 2023 10:29:11

Additional context

N.A.

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