default top-level `await` should have .medium priority

[dyumin]

Hi! It seems that @main starts main task with medium priority, there is no need to change that.

https://github.com/apple/pir-service-example/blob/1a0747b1dae7325df8b439a9782ceb68ea35e73a/Sources/PIRService/main.swift#L55C37-L55C50