[export_cpp] Conv2D export bug with in_channels or out_channels > 1
## What commit version of aidge do you use
- `aidge_export_cpp`: aidge_export_cpp@9f86629bbc179698a89b4a85d2bc79a567a04522
## Problem description
2D convolution export gives wrong results with in_channels\>1
## Reproducible example code
From `test_export.py` , the first test with on in_channel passes, the second with 2 in_channels fails.
```python
def test_Conv(self):
model = aidge_core.sequential([
aidge_core.Conv2D(1, 1, [3, 3], name="InputNode")
])
initFiller(model)
self.unit_test_export(model, "Conv", [[1, 1, 9, 9]]) # IS OK
```
or
```c++
def test_Conv_in_channels2(self):
model = aidge_core.sequential([
aidge_core.Conv2D(2, 2, [3, 3], name="InputNode")
])
initFiller(model)
self.unit_test_export(model, "Conv", [[1, 2, 9, 9]]) # ERROR !
```
issue