No active repository found on empty workspace

[osortega]

Testing #290457

Steps:

1. Open VS Code on an empty workspace
2. Select any of the cloud sessions
3. Click on Checkout
4. 🐛 Error pops up
5. Install the extension
6. 🐛 checkout button disappears

I'm not sure how hard this would be to fix since I believe the GHPR extension scopes session PRs to the current repository, maybe the easiest would be to disable this on empty workspace?