feat: add --test-report flag and fix PyGithub auth

[YuanYuYuan]

Summary

• Fix PyGithub >= 2.0 compatibility: the deprecated Github(token) positional argument no longer authenticates; switch to Github(auth=Auth.Token(token))
• Add --test-report <ci_launcher_url> flag to fetch JUnit results from a completed ci_launcher run and post a structured summary comment on the PR

Key Changes

• ros_github_scripts/ci_for_pr.py: PyGithub auth fix; new --test-report flag with parse_child_build_urls, fetch_child_build_urls, fetch_test_report, and format_test_report_comment helpers

Example output

--test-report posts a comment like this one on ros2/rmw_zenoh#987:
ros2/rmw_zenoh#987 (comment)

The comment includes:

• A summary table with pass/fail counts, build duration, and a direct link to each platform's test report page
• Collapsible per-platform failure tables sorted by package name

Usage

# Step 1 — trigger the build (existing flow)
ros-ci-for-pr --pulls ros2/rmw_zenoh#987 --target lyrical --packages rmw_zenoh_cpp --build --comment

# Step 2 — after builds complete (~1-2h), post the test report
ros-ci-for-pr --pulls ros2/rmw_zenoh#987 --test-report https://ci.ros2.org/job/ci_launcher/19468 --comment