[v6.d REVIEW] Fix up .pairup throwage test
[v6.d REVIEW] Fix up .pairup throwage test

Currently we rely on `dies-ok` sinking the returned Seq.
Fix by sinking it ourselves and also test the exception type.

Orig: https://github.com/perl6/roast/commit/37c8fd4c0

dogbert17/roast,perl6/roast,dogbert17/roast