NIOSSHClient gets stucked

# Problem
When testing [NIOSSHClient](https://github.com/apple/swift-nio-ssh/blob/main/Sources/NIOSSHClient/main.swift), I am always getting stucked indefinitely on childChannel wait() method. Could somebody help me understand what is the problem?

# Findings
- promise.FutureResult was created successfully, but my guess is, it was never met.
- ExampleExecHandler was never activated and command was never executed.

# Setup
- Testing on M1 Macbook Pro with latest MacOS & XCode

Start with Sources/NIOSSHClient/main.swift and reproduce the indefinite wait at childChannel wait(). Trace the promise.FutureResult and ExampleExecHandler activation, then confirm that the command executes and the child channel completes instead of remaining stuck.

Written by the indexing model from the issue text.