COPILOT_CUSTOM_INSTRUCTIONS_DIRS failing to load *.instructions.md

### Describe the bug

Setting the COPILOT_CUSTOM_INSTRUCTIONS_DIRS as a user-level environment variable does not produce the expected results as per the documentation. Instructions at the location specified are not loading.

### Affected version

GitHub Copilot CLI 1.0.3.

### Steps to reproduce the behavior

1. Set COPILOT_CUSTOM_INSTRUCTIONS_DIRS in Windows environment to %APPDATA%\Code\User\prompts
2. Load Copilot
3. /instructions, the instructions from this did not load.

### Expected behavior

Setting the COPILOT_CUSTOM_INSTRUCTIONS_DIRS should load *.instructions.md files from this location. This does not happen.

### Additional context

_No response_