Can't assign Copilot when creating new issue from GHPRI directly

[bamurtaugh]

Using latest VS Code Insiders and GHPRI pre-release extension:

• Open GHPRI view
• + to Create an Issue
• Set Assignees: @copilot
• ❓ Creating issue failed:

This seems like a different scenario than what #6742 supports (as that supports assigning Copilot to an already-created issue)?