fix markup mixup

Author: gfldex

doc/Type/Signature.pod

@@ -423,7 +423,7 @@ However, this unpacking of objects as their attributes is only the default
 behavior. To make an object get destructured differently, change its
 L<C<Capture>> method.
 
-=head2 C<Long Names>
+=head2 X<Long Names>
 
 To avoid to have some arguments to be considered for multiple dispatch
 separate them with a double semi-colon.