Conformer_Transducer's encoder exported to ONNX fails to instantiate an `onnxruntime.InferenceSession`
**Describe the bug**

Creating an onnx `InferenceSession` using the exported encoder from a conformer_transducer model (using the default parameters of `export`) leads to an `ONNXRuntimeError`.

```
[ONNXRuntimeError] : 1 : FAIL : Load model from /tmp/tmp_ssi0eq1/encoder-test.onnx failed:Type Error: Type parameter (Tind) of Optype (Slice) bound to different types (tensor(int32) and tensor(int64) in node (/pos_enc/Slice).
```

**Steps/Code to reproduce bug**

Here's a minimal example to reproduce the bug.

```python
#! /usr/bin/env python3
# -*- coding: utf-8 -*-

import tempfile
import onnxruntime as ort
from nemo.collections.asr.models import EncDecRNNTBPEModel


def main():
    model = EncDecRNNTBPEModel.from_pretrained(
        "stt_fr_conformer_transducer_large"
    )

    with tempfile.TemporaryDirectory() as temp_dir:
        model.export(temp_dir + "/test.onnx")

        try:
            ort.InferenceSession(temp_dir + "/encoder-test.onnx")
            print("encoder has been sucessfully initialized")
        except Exception as e:
            print("Error on encoder")
            print(e)

        try:
            ort.InferenceSession(temp_dir + "/decoder_joint-test.onnx")
            print("decoder_joint has been sucessfully initialized")
        except Exception as e:
            print("Error on decoder_joint")
            print(e)


if __name__ == "__main__":
    main()
```

**Expected behavior**

Well... The `InferenceSession` should be correctly initialized from the exported onnx file, shouldn't it ?

**Environment overview and details**

 - Environment location:

 - Method of NeMo install:
```
> conda create -n NeMo python==3.9
> pip install Cython
> pip install "nemo_toolkit[all]"
```

- OS version
```
> uname -srvpio
Linux 6.0.9-arch1-1 #1 SMP PREEMPT_DYNAMIC Wed, 16 Nov 2022 17:01:17 +0000 unknown unknown GNU/Linux
```
- PyTorch version
```
> python
>>> import torch
>>> torch.__version__
'1.13.0'
```
- Python version
```
> python --version
Python 3.9.0
```
