Add belongs_to :project to Geo::ProjectRegistry

app/models/geo/project_registry.rb

 class Geo::ProjectRegistry < Geo::BaseRegistry
-  validates :project_id, presence: true
+  belongs_to :project
+
+  validates :project, presence: true
 
   scope :failed, -> { where.not(last_repository_synced_at: nil).where(last_repository_successful_sync_at: nil) }
   scope :synced, -> { where.not(last_repository_synced_at: nil, last_repository_successful_sync_at: nil) }

spec/models/geo/project_registry_spec.rb

 require 'spec_helper'
 
 describe Geo::ProjectRegistry, models: true do
+  describe 'relationships' do
+    it { is_expected.to belong_to(:project) }
+  end
+
   describe 'validations' do
-    it { is_expected.to validate_presence_of(:project_id) }
+    it { is_expected.to validate_presence_of(:project) }
   end
 end