[perl #77338] [BUG] Rakudo erroneously parses some optional-parameter question marks as twigils

[Christian Bartolomaeus via RT]

The tests are in S06-signature/optional.t and S14-roles/parameterized-basic.t, 
respectively. They were added with the following commit: 
https://github.com/perl6/roast/commit/2b3bee5223