[BUG]: bad error message for SpeedControllerGroup construction

[virtuald]

Problem description

The error message generated is useless, we should fix it.

Operating System

Windows, MacOS, Linux, RoboRIO

Installed Python Packages

No response

Reproducible example code

>>> import wpilib
>>> wpilib.SpeedControllerGroup(1,2,3)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: Unable to cast Python instance to C++ type (compile in debug mode for details)