Auto merge failure messages should be posted by the system, not the user

One of the system notes generated by the merge trains feature looks like this:

Ideally, this message would read:

This merge request was removed from the merge train because no stages and/or jobs exist for this pipeline.

and not include

Administrator @root

In its current form, the message implies the action was initiated by the user (Administrator @root) when in fact this action was performed automatically by the system.