Fix TypeError when iterating MS1MV3 dataset

[vinhtq115]

Recently, I tried training with MS1MV3 dataset but I always encountered this exception:

Exception in thread Thread-3:
Traceback (most recent call last):
  File "/home/tran.quang.vinh/miniconda3/envs/gnn/lib/python3.10/threading.py", line 1009, in _bootstrap_inner
    self.run()
  File "/mnt/disk2/tran.quang.vinh/FR/insightface/recognition/arcface_torch/dataset.py", line 89, in run
    for item in self.generator:
  File "/home/tran.quang.vinh/miniconda3/envs/gnn/lib/python3.10/site-packages/torch/utils/data/dataloader.py", line 681, in __next__
    data = self._next_data()
  File "/home/tran.quang.vinh/miniconda3/envs/gnn/lib/python3.10/site-packages/torch/utils/data/dataloader.py", line 1376, in _next_data
    return self._process_data(data)
  File "/home/tran.quang.vinh/miniconda3/envs/gnn/lib/python3.10/site-packages/torch/utils/data/dataloader.py", line 1402, in _process_data
    data.reraise()
  File "/home/tran.quang.vinh/miniconda3/envs/gnn/lib/python3.10/site-packages/torch/_utils.py", line 461, in reraise
    raise exception
TypeError: Caught TypeError in DataLoader worker process 0.
Original Traceback (most recent call last):
  File "/home/tran.quang.vinh/miniconda3/envs/gnn/lib/python3.10/site-packages/torch/utils/data/_utils/worker.py", line 302, in _worker_loop
    data = fetcher.fetch(index)
  File "/home/tran.quang.vinh/miniconda3/envs/gnn/lib/python3.10/site-packages/torch/utils/data/_utils/fetch.py", line 49, in fetch
    data = [self.dataset[idx] for idx in possibly_batched_index]
  File "/home/tran.quang.vinh/miniconda3/envs/gnn/lib/python3.10/site-packages/torch/utils/data/_utils/fetch.py", line 49, in <listcomp>
    data = [self.dataset[idx] for idx in possibly_batched_index]
  File "/mnt/disk2/tran.quang.vinh/FR/insightface/recognition/arcface_torch/dataset.py", line 166, in __getitem__
    label = torch.tensor(label, dtype=torch.long)
TypeError: 'numpy.float32' object cannot be interpreted as an integer

This PR simply converts label from float to int in order to fix the above exception.