Fix `Mu` as is default() on attributes
Fix `Mu` as is default() on attributes

Fixes RT#132082: https://rt.perl.org/Ticket/Display.html?id=132082

Routine args default to `Any`, so the multi for is default
with Mu was never reached, instead going to the multi that
cries about unknown traits.

awwaiid/rakudo,labster/rakudo,tony-o/rakudo,tony-o/rakudo,lucasbuchala/rakudo,softmoth/rakudo,nbrown/rakudo,rakudo/rakudo,salortiz/rakudo,rakudo/rakudo,labster/rakudo,nbrown/rakudo,lucasbuchala/rakudo,softmoth/rakudo,salortiz/rakudo,MasterDuke17/rakudo,usev6/rakudo,salortiz/rakudo,lucasbuchala/rakudo,awwaiid/rakudo,rakudo/rakudo,nbrown/rakudo,nbrown/rakudo,awwaiid/rakudo,softmoth/rakudo,raydiak/rakudo,labster/rakudo,tbrowder/rakudo,usev6/rakudo,tbrowder/rakudo,tbrowder/rakudo,usev6/rakudo,tbrowder/rakudo,tony-o/rakudo,MasterDuke17/rakudo,nbrown/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,awwaiid/rakudo,nbrown/rakudo,salortiz/rakudo,tony-o/rakudo,lucasbuchala/rakudo,Gnouc/rakudo,labster/rakudo,salortiz/rakudo,raydiak/rakudo,raydiak/rakudo,Gnouc/rakudo,MasterDuke17/rakudo,rakudo/rakudo,tony-o/rakudo,Gnouc/rakudo,labster/rakudo,rakudo/rakudo,Gnouc/rakudo,usev6/rakudo,Gnouc/rakudo,usev6/rakudo,awwaiid/rakudo,tbrowder/rakudo,labster/rakudo,salortiz/rakudo,lucasbuchala/rakudo,tony-o/rakudo,softmoth/rakudo,raydiak/rakudo,softmoth/rakudo,Gnouc/rakudo,rakudo/rakudo,MasterDuke17/rakudo