Allow updating of project auto devops settings

Updating didn't work, as the project_id was missing to be set for the
project_auto_devops model.

Fixes gitlab-org/gitlab-ce#37893

app/models/project.rb

@@ -192,7 +192,7 @@ class Project < ActiveRecord::Base
   accepts_nested_attributes_for :variables, allow_destroy: true
   accepts_nested_attributes_for :project_feature
   accepts_nested_attributes_for :import_data
-  accepts_nested_attributes_for :auto_devops
+  accepts_nested_attributes_for :auto_devops, update_only: true
 
   delegate :name, to: :owner, allow_nil: true, prefix: true
   delegate :members, to: :team, prefix: true

changelogs/unreleased/zj-update-project-settings.yml

+---
+title: Allow updating of project auto devops settings
+merge_request:
+author:
+type: fixed

spec/controllers/projects/pipelines_setttings_controller_spec.rb

+require 'spec_helper'
+
+describe Projects::PipelinesSettingsController do
+  set(:user) { create(:user) }
+  set(:project_auto_devops) { create(:project_auto_devops) }
+  let(:project) { project_auto_devops.project }
+
+  before do
+    project.add_master(user)
+
+    sign_in(user)
+  end
+
+  describe 'PATCH update' do
+    before do
+      patch :update,
+        namespace_id: project.namespace.to_param,
+        project_id: project,
+        project: {
+          auto_devops_attributes: { enabled: false, domain: 'mempmep.md' }
+        }
+    end
+
+    context 'when updating the auto_devops settings' do
+      it 'redirects to the settings page' do
+        expect(response).to have_http_status(302)
+        expect(flash[:notice]).to eq("Pipelines settings for '#{project.name}' were successfully updated.")
+      end
+    end
+  end
+end