Ensure goniometer can be stored/restored with NexusDetectors

[kif]

Found on BM02

[kif]

I suspect this is the same bug:

> gonioref.sload(json_file)#, gonioref
> 
> ===============================================================
> 
> ---------------------------------------------------------------------------RuntimeError
>                              Traceback (most recent call
> last)<ipython-input-40-dbbf7a4eb1b1> in <module>      1
> print(open(json_file).read())      2 ----> 3
> gonioref.sload(json_file)#, gonioref
> ~/miniconda3/envs/pyfai/lib/python3.9/site-packages/pyFAI/goniometer.py
> in sload(cls, filename, pos_function)    845                 funct =
> ExtendedTransformation(**tansfun)    846             else:--> 847
>            raise RuntimeError("content= %s, not in in
> (GeometryTranslation, GeometryTransformation, ExtendedTranformation)")
>    848         else:  # assume GeometryTransformation    849
>   funct = GeometryTransformation(**tansfun)
> RuntimeError: content= %s, not in in (GeometryTranslation,
> GeometryTransformation, ExtendedTranformation)
>