fix tensor dimensions are not compatible for FP8 issue in sft
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---

Your code was analyzed with PyLint. The following annotations have been identified:

```
************* Module nemo.collections.nlp.data.language_modeling.megatron.gpt_sft_chat_dataset
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:113:0: C0301: Line too long (165/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:116:0: C0301: Line too long (144/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:147:0: C0301: Line too long (132/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:156:0: C0301: Line too long (165/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:177:0: C0301: Line too long (169/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:240:0: C0301: Line too long (124/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:59:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:182:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:311:0: C0115: Missing class docstring (missing-class-docstring)

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```

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# What does this PR do ?
when we use nemo for sft FP8 training, it will reports 
`  File "/usr/local/lib/python3.10/dist-packages/torch/autograd/function.py", line 289, in apply
    return user_fn(self, *args)
  File "/usr/local/lib/python3.10/dist-packages/transformer_engine/pytorch/module/linear.py", line 447, in backward
    wgrad, _ = fp8_gemm(
  File "/usr/local/lib/python3.10/dist-packages/transformer_engine/pytorch/cpp_extensions/gemm.py", line 45, in fp8_gemm
    assert_dim_for_fp8_exec(A)
  File "/usr/local/lib/python3.10/dist-packages/transformer_engine/pytorch/utils.py", line 221, in assert_dim_for_fp8_exec
    assert check_dim_for_fp8_exec(tensor), (
AssertionError: Tensor dimensions are not compatible for FP8 execution: (3584 % 8 != 0, 1912 % 16 != 0)` 

 fp8 GEMM requires tensor dimension be multiple of 16. This means the sequence dimension of input data should be padded to multiple of 16, which is not implemented in NeMo chat style data loader yet.​
so need to change 
`max_length = min(self.max_seq_length, self._ceil_to_nearest(max_length, 8)`
to
`max_length = min(self.max_seq_length, self._ceil_to_nearest(max_length, 16)`
Add a one line overview of what this PR aims to accomplish.

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