adds a test that illustrates #55 - env not getting set on remote execution with stream

[heckj]

I ran across #55 and thought I'd try and verify it to start to debug it.

There's a lot in here that I'm not familiar with, but I thought first step would be to reproduce the issue in a test, so I tried to loosely replicate the issue in question interacting with the OpenSSH docker-service setup that's outlined in the CI with GH actions.

In addition to running the service locally using the command:

docker run -d -p 2222:2222 -e USER_NAME=citadel -e USER_PASSWORD=hunter2 -e PASSWORD_ACCESS=true lscr.io/linuxserver/openssh-server:latest

I invoked the tests with:

#!/usr/bin/env bash
set -eoux pipefail

export SWIFT_DETERMINISTIC_HASHING=1
export SSH_HOST=localhost
export SSH_PORT=2222
export SSH_USERNAME=citadel
export SSH_PASSWORD=hunter2

swift test

[Joannis]

Thanks for this PR!