Fix false PR event warnings for issue number collisionsFix false PR event warnings when issue numbers overlap with PR numbers (#3762)

[Noaman-Akhtar]

Fixes #3762.

What changed

• Updated BulkGithubEventCollection._process_pr_events in augur/tasks/github/events.py.
• When related PR URL is missing from local PR map:
  • Parse PR number from URL
  • Check if that number exists in repo issues (gh_issue_number)
  • If yes, skip silently (expected due to shared GitHub issue/PR numbering)
  • If no, keep existing warning

Why

GitHub uses a shared namespace for issue and PR numbers. The old logic emitted noisy warnings for valid issue numbers that are not PRs.

Tests

Added tests/test_tasks/test_github_tasks/test_events.py:

• skips warning when missing PR number matches existing issue number
• still warns when PR number is missing from both PR and issue data