Marketplace for plugins on windows is broken

### Describe the bug

On windows Powershell or CMDline (not WSL2) internal custom marketplace plugins are being looked for in the wrong place (root dir)

### Affected version

0.421

### Steps to reproduce the behavior

when adding an internal marketplace via /plugin marketplace add https://orgname.ghe.com/reponame.git
the cli subsequently fails when using /plugin install plgunname@internal-marketplace
with 'Not found'

### Expected behavior

plugin is installed

### Additional context

Issue appears to be that the CLI is looking in the root directory of the marketplace, not in the /plugins folder.
The same commands and config work on Mac.