flutter-devicelab-mac-4 and flutter-devicelab-mac-5 are now in the staging pool as of #79430. Promote to the prod pool once all existing tests pass on those machines.

https://chromium-swarm.appspot.com/bot?id=flutter-devicelab-mac-4
https://chromium-swarm.appspot.com/bot?id=flutter-devicelab-mac-5

Blocked by #85654.