Move some `Mac_arm64_ios` bot capacity from staging pool (5 bots) to try pool (1 bot)

[jmagman]

To start running Mac_arm64_ios run_debug_test_macos in presubmit again, more bots should be allocated to the try pool.

1 bot:
https://chromium-swarm.appspot.com/botlist?f=device_os%3AiOS-16&f=os%3AMac-12&f=cpu%3Aarm64&f=pool%3Aluci.flutter.try

Staging has 5 unused bots

https://chromium-swarm.appspot.com/botlist?c=id&c=task&c=os&c=status&d=asc&f=device_os%3AiOS-16&f=os%3AMac-12&f=cpu%3Aarm64&f=pool%3Aluci.flutter.staging&k=pool&s=id

Move at least a few to the try pool.

Unblocks #125341.
See #118827 and #118828.

[jmagman]

cc @yusuf-goog

[jmagman]

@yusuf-goog, @vashworth is going to take over #125341, let her know if you need any other info to load balance these bots.

[keyonghan]

@yusuf-goog We may want to make sure the staging bots are in a good state before moving.

[jmagman]

I'm going to close #125341 for now, when this issue is complete it can be resurrected.