pr-review fails to find linked PR when linked via 'Closes #N' keyword

[ellen-goc]

Bug Report

Description

askcc pr-review fails with No linked pull request found for issue #N in owner/repo even when the PR is properly linked to the issue via a closing keyword (Closes #N) in the PR body.

Steps to Reproduce

1. Create a PR with Closes #20 in the body
2. Run: askcc --cwd /path/to/repo pr-review -g https://github.com/weyucou/sops/issues/20

Expected Behavior

askcc should find the linked PR via GitHub's API and proceed with the review.

Actual Behavior

ValueError: No linked pull request found for issue #20 in weyucou/sops

Environment

• Issue: https://github.com/weyucou/sops/issues/20
• PR: https://github.com/weyucou/sops/pull/31 (has Closes #20 in body)
• GitHub timeline API does show the cross-reference link correctly

Notes

The GitHub GraphQL API correctly returns the PR as a CrossReferencedEvent in the issue's timeline:

{"__typename":"CrossReferencedEvent","source":{"__typename":"PullRequest","number":31}}

It appears askcc may not be checking the timeline API for cross-references.