Fix RSpec/DescribedClass cop (#25104)

spec/models/identity_spec.rb

@@ -12,7 +12,7 @@ RSpec.describe Identity do
     end
 
     it 'returns an instance of Identity' do
-      expect(described_class.find_for_oauth(auth)).to be_instance_of Identity
+      expect(described_class.find_for_oauth(auth)).to be_instance_of described_class
     end
   end
 end