TestRunner.bs: `event` might be `invalid` when debugging tests

[markwpearce]

https://github.com/rokucommunity/rooibos/blob/295c0d2c62f4f02be2b9cd5ae96a16b75dbae5a0/framework/src/source/rooibos/TestRunner.bs#L243C5-L244C32

Sometimes when the debugger is active, wait(0, port) might return invalid. Perhaps this could be changed to a loop:

event = invalid
while event = invalid
  event = wait(0, port)
end while