Fix job links in Slack report
# What does this PR do?

The current `notification_service.py` doesn't take `artifact_path['gpu']` (`single` or `multi`) into account when storing the `job_link` information, which leads to wrong pages (sometimes) when we click the `GitHub Action Job` button on Slack.

This PR fixes this issue.
_The documentation is not available anymore as the PR was closed or merged._