Add a test for rakudo/rakudo#3299 Proc::Async memory corruption bug.
Add a test for rakudo/rakudo#3299 Proc::Async memory corruption bug.

There are 1200 iterations of a loop to try to reproduce the memory corruption bug.
Without the fix, typically fails after 500-800 iterations.
With the fix, takes about 13 seconds on my machine for all 1200 iterations.

perl6/roast,dogbert17/roast,dogbert17/roast