[perl #65904] Providing a sub signature with an invocant makes Rakudo emit an imcc syntax error

[Carl Mäsak]

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<masak> rakudo: sub foo($bar:) {};
<p6eval> rakudo 79d0b9: OUTPUT«error:imcc:syntax error, unexpected
IDENTIFIER ('self') [...]
* masak submits rakudobug

Expected: a syntax error from somewhere higher than the Parrot internals.