update_pull_request: `reviewers` field silently ignores team slugs

[dastrobu]

The update_pull_request tool's reviewers field silently ignores team reviewer slugs (e.g., ORG/team-slug). No error is returned, but the teams are not added as reviewers on the pull request.

Steps to Reproduce

1. Create a pull request in an organization repository
2. Call update_pull_request with reviewers set to team slugs:

   {
     "owner": "MY-ORG",
     "repo": "my-repo",
     "pullNumber": 123,
     "reviewers": ["MY-ORG/my-team"]
   }

3. Verify review requests on the PR — they are empty

Expected Behavior

Either:

• The reviewers field should support team slugs (in ORG/team-slug format) and correctly call the GitHub API's team_reviewers parameter, OR
• A separate team_reviewers field should be exposed on the tool, OR
• An error should be returned indicating that team slugs are not supported

Actual Behavior

The tool returns a success response but no team review requests are created. The failure is silent.

Notably, when passing an invalid individual username, the API correctly returns a 422 error:

Reviews may only be requested from collaborators. One or more of the users or teams you specified is not a collaborator of the repository.

But team slugs are silently dropped before reaching the API — no error is surfaced.

Environment

Tested and reproduced on:

• GitHub Enterprise Server (GHES) 3.19.4
• GitHub Enterprise Cloud (EU data residency, ghe.com)

MCP server version: ghcr.io/github/github-mcp-server:latest (pulled 2025-05-07, digest sha256:2ac27ef03461ef2b877031b838a7d1fd7f12b12d4ace7796d8cad91446d55959)

Workaround

Using the gh CLI works correctly:

gh pr edit 123 --add-reviewer ORG/team-slug

Context

The GitHub REST API for [requesting reviewers](https://docs.github.com/en/rest/pulls/review-requests#request-reviewers-for-a-pull-request) distinguishes between reviewers (array of user logins) and team_reviewers (array of team slugs). The MCP server tool currently only exposes a single reviewers field described as "GitHub usernames to request reviews from", with no support for teams.