Do not enforce PowerShell on Windows

### Describe the bug

I have a perfectly capable `cmd` terminal, running copilot in it is incapable of running for example `gradlew`. That command does not require a powershell, it's a simple batch file.

### Affected version

0.0.392 Commit: cefb35e

### Steps to reproduce the behavior

copilot -i "Run gradlew build and fix errors"

### Expected behavior

Just works, regardless of powershell being installed or not.

### Additional context

_No response_