Remove User#triggers dependent: :destroy

This does not appear to be necessary. It was first added in
https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/9713#note_24835526
and there does not appear to be any justification for this as there is
already a cascading foreign key delete. There don't appear to be any
`before_destroy` or similar steps that might benefit from this
`dependent: :destroy` so it seems safe to remove it.

app/models/user.rb

@@ -187,7 +187,7 @@ class User < ApplicationRecord
   has_many :todos
   has_many :notification_settings
   has_many :award_emoji,              dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
-  has_many :triggers,                 dependent: :destroy, class_name: 'Ci::Trigger', foreign_key: :owner_id # rubocop:disable Cop/ActiveRecordDependent
+  has_many :triggers,                 class_name: 'Ci::Trigger', foreign_key: :owner_id
 
   has_many :issue_assignees, inverse_of: :assignee
   has_many :merge_request_assignees, inverse_of: :assignee

spec/models/user_spec.rb

@@ -109,7 +109,6 @@ RSpec.describe User do
     it { is_expected.to have_many(:spam_logs).dependent(:destroy) }
     it { is_expected.to have_many(:todos) }
     it { is_expected.to have_many(:award_emoji).dependent(:destroy) }
-    it { is_expected.to have_many(:triggers).dependent(:destroy) }
     it { is_expected.to have_many(:builds).dependent(:nullify) }
     it { is_expected.to have_many(:pipelines).dependent(:nullify) }
     it { is_expected.to have_many(:chat_names).dependent(:destroy) }