validTest.py did not pass, since we use `SINK3_F`.
I initially tried swapping the order
```
args = (arg1, arg2) # $ arg1 arg2 func=starargs_only
more_args = (arg4, arg3)
starargs_only(*args, *more_args)
```
But then asked myself, what is it _actually_ we're testing here? and it
seems to be the way we handle multiple *args arguments in the same call,
so I converted the test to be that instead! (and it matches what we do
in test_stararg_mixed)
63b2bd0871