Add a workaround for people that use *args instead of listing (#166883)
parameters when defining the scripting interfaces.
We try to count the parameters to make sure the user has defined them
correctly, but this throws the counting off.
I'm not adding a test for this because then it would seem like we
thought this was a good idea. I'd actually rather not support it
altogether, but we added the parameter checking pretty recently so there
are extant implementations that we broke. I only want to support them,
not suggest anyone else do this going forward.