Add a spec for Admin::ActionLog (#9775)

spec/models/admin/action_log_spec.rb

+# frozen_string_literal: true
+
 require 'rails_helper'
 
 RSpec.describe Admin::ActionLog, type: :model do
+  describe '#action' do
+    it 'returns action' do
+      action_log = described_class.new(action: 'hoge')
+      expect(action_log.action).to be :hoge
+    end
+  end
 end