In merged result pipelines the merge ref
carries a merge commit whose author
is always the merge request creator
and not an authenticated user
(such as the pushing or pipeline
trigger user)

See the override to current_user in the following link:
https://gitlab.com/gitlab-org/gitlab/blob/b535f1ff45c8d661ba1c9818b26f5a41b32ae5ad/app/services/merge_requests/mergeability_check_service.rb#L160
as a reference for this change.

This behavior is important to note in case users
rely in author related variables in the pipelines
and observe the behavior of it never changing
despite different users pushing to the same
source branch.