Fails when run normally but works with MVM_SPESH_DISABLE=1

test.pl6

use nqp;
{
    constant $read-file = "README.md".IO;
    $read-file.IO.r; 

    for ^1000 {
        my $p = Proc::Async.new( | «/bin/cat    $read-file» );
        my $output = '';
        $p.stdout.tap: -> $s { $output ~= $s; };
        await $p.start;
    nqp::force_gc();	
    }
}