[perl #119919] LTA Error Message for operator declaration with []

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<lue> r: sub infix:["@"] ($a, $b) { "$a@$b" }; say "me"@"server"
<camelia> rakudo f86a1a: OUTPUT«===SORRY!===␤No such method 'ast' for 
invocant of type 'NQPMu'␤»

The infix:["..."] form of declaration should at least have a better 
error message.