Axis attribute of Concat is not changed by adapt_to_backend

Context

The Export CPP handles NHWC tensors while aidge tensors are NCHW by default.
That's why the adapt_to_backend() function was recently added, it allows to set the format for each node of a specific backend, then when calling this function the dimensions are changed (and intermediate tensors transposed).

Issue

This does not seem to work for the axis attribute of the Concat node :

Here the axis should be 3 isntead of 1.