Fix nil pointer issue when pipeline schedule owner is deleted

Vinay Shelkerequested to merge
gitlab-community/gitlab-org/terraform-provider-gitlab:fix-nil-owner-pipeline-schedule into main

When a pipeline schedule owner user is deleted from GitLab, the API returns null for the owner field. The datasource was crashing with a nil pointer dereference when trying to access owner fields.

Added nil check for schedule.Owner in both datasources following the same pattern used for LastPipeline. Added acceptance tests that reproduce the original bug by creating a schedule as a user then deleting that user.

Fixes #6782 (closed)

Merge request reports