`@githubpr` doesn't know PR assignees

[bamurtaugh]

Using latest VS Code Insiders, GHPRI and Copilot Chat pre-release, Windows 11.

Steps to Reproduce:

1. Open https://github.com/microsoft/vscode-pull-request-github in VS Code Insiders
2. Ask @githubpr who is assigned to the currently open pr 7317 (I opened the PR overview page, but I didn't check out the PR)
   • Copilot says there are no assignees (which is incorrect, since Add Cancel Review button to review submission interface #7317 has assignees)
   • I suppose this is due to Ability to add an open (but not checked out) PR as context to chat #7332
3. Check out the PR with GHPRI
4. Ask @githubpr who is assigned to the currently open pr 7317 again
5. ❓ I'm still told the PR has no assignees or reviewers

Here are screenshots of both parts of the conversation (pre-checkout, and with checkout):

The input looks like both queries tried to fetch for an issue rather than PR (since it says issueNumber), though the output looks like it did get the correct PR based on owner, repo, title, and body:

[alexr00]

Somehow we just never added author, assignees, or reviewers.

[alexr00]

To verify:

• Install the latest pre-release
• Check out a PR from the PRs view
• Open the Chat view and use @githubpr to ask some questions about current PRs assignees
• Verify @githubpr answers correctly about the current PRs assignees.

[bamurtaugh]

This works! I tried it on a couple PRs. Interestingly, sometimes it actually links to the assignee's GH profile on the web, and other times it just prints their name: