The test is more complex than the code if you want to accept both [0,1] and [1,0] better and easier just rely on the expected sum. Anyway..

sub two_sum_Discipulus {
    my ($input, $target) = @_;
    foreach my $index ( 0 .. $#$input ){
        ( $_ != $index and $input->[$_] + $input->[$index] == $target 
+) ? 
                return [$index, $_]                                   
+  :   0 
                for 0 .. $#$input;
    }
}
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PS added newlines for a minimal readability enhancement

L*