Fix Powershell spawned from Command Prompt being mis-detected

[spowelljr]

Description

Fixes #4891

Issue:

For CI testing Windows in minikube we SSH into a Windows machine, which starts us in Command Prompt. We then run powershell to change the terminal to Powershell. However, within the Powershell terminal the SHELL environment variable is still pointing to Command Prompt (c:\windows\system32\cmd.exe). So when running the exported function shell.Detect here it returns cmd instead of the expected powershell.

If cmd is detected via SHELL environment variable, do the the more in-depth shell detection.

Related issue(s)

#4891