[perl #128783] invocant not allowed in signature literals

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# New Ticket Created by  Wenzel Peppmeyer 
# Please include the string:  [perl #128783]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=128783 >


my $m = method ($a: $b){}; say $m ~~ :($a: $b);
# OUTPUT«===SORRY!=== Error while compiling <tmp>␤Can only use the : invocant 
marker in the signature for a method␤at <tmp>:1␤------>  method ($a: $b){}; say 
$m ~~ :($a: $b⏏);␤    expectig any of:␤        constraint␤»
# expected output:
True