When joining curves, the resulting curve will inherit the bevel depth of
the active curve, but the radii would stay the same which leads to
changed appearance when joining.

Now compensate for this taking the different bevel depths into account (if present) and scaling the radii accordingly.

Was a feature request here (and I also think we had reports about this which were usually turned down as not-a-bug):
https://blender.community/c/rightclickselect/bhhbbc/