[perl #124922] Roast rakudo skip/todo test:./S06-signature/named-parameters.t line:256 reason: 'where constraints'

[Christian Bartolomaeus via RT]

This test tried to set positional parameters by passing named arguments. Since 
this feature went away, I adjusted and unfudged the test: 
https://github.com/perl6/roast/commit/a9f6adf01a