CI: resolve PR author in community team check

[rogerbarreto]

Motivation

The Limit community pull requests workflow fails on team_check with 401 Bad credentials when a community PR is opened. The shared check_team_membership.js script looks for the author on payload.issue, but pull_request_target events expose the author on payload.pull_request instead. The script then falls back to issues.get, which fails.

DevFlow PR Review already reads payload.pull_request.user.login and succeeds on the same events.

Changes

• Resolve author from payload.pull_request.user.login before API fallback
• Use pulls.get when resolving from a PR context
• Add unit tests for pull_request payload and pulls.get fallback

Validation plan

After merge:

1. Close and reopen a community PR (e.g. .NET: Preserve UTF-8 order in HeadTailBuffer #7128) to re-trigger limit-community-prs
2. Confirm team_check is green and logs Author <login> is not a team member

Fixes the CI failure seen in run https://github.com/microsoft/agent-framework/actions/runs/29404637576

[Copilot]

Pull request overview

Fixes the “Limit community pull requests” workflow failing on pull_request_target by correctly resolving the PR author from context.payload.pull_request (and using the PR API fallback when in a PR context), aligning behavior with the existing DevFlow PR Review workflow.

Changes:

• Resolve author from context.payload.pull_request.user.login before making API calls.
• When in a PR context, fall back to github.rest.pulls.get instead of issues.get.
• Extend unit tests to cover pull_request payload author resolution and pulls.get fallback.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
.github/scripts/check_team_membership.js	Updates author resolution to support pull_request_target payloads and uses pulls.get fallback for PR contexts.
.github/tests/test_check_team_membership.js	Adds tests for author resolution via payload.pull_request and via pulls.get fallback when needed.