Support system & system_action fields for merge event attributes
These fields are available since 18.6: https://about.gitlab.com/releases/2025/11/20/gitlab-18-6-released/#webhook-triggers-for-system-initiated-approval-resets
Edited by Artem Mikheev
These fields are available since 18.6: https://about.gitlab.com/releases/2025/11/20/gitlab-18-6-released/#webhook-triggers-for-system-initiated-approval-resets