publish-sylva-units-artifact runs in full mode in child pipelines from MR

!7355 (merged) fixed publish-sylva-units-artifact to run in ensure mode for MR pipelines using CI_PIPELINE_SOURCE == "merge_request_event".But this condition only matches the parent MR pipeline.

When deployment pipelines are triggered as child pipelines from an MR pipeline, CI_PIPELINE_SOURCE is set to parent_pipeline, not merge_request_event. This causes the job to run in full mode.