Remove dependent => :destroy

app/models/ci/pipeline_schedule.rb

@@ -9,7 +9,7 @@ module Ci
     belongs_to :owner, class_name: 'User'
     has_one :last_pipeline, -> { order(id: :desc) }, class_name: 'Ci::Pipeline'
     has_many :pipelines
-    has_many :variables, :dependent => :destroy, class_name: 'Ci::PipelineScheduleVariable'
+    has_many :variables, class_name: 'Ci::PipelineScheduleVariable'
 
     validates :cron, unless: :importing?, cron: true, presence: { unless: :importing? }
     validates :cron_timezone, cron_timezone: true, presence: { unless: :importing? }