Fix order-dependent runner_spec.rb

spec/models/runner_spec.rb

@@ -34,15 +34,12 @@ describe Runner do
       let(:runner_management_config) { {runner_management: {enabled: true, strategy: strategy}} }
 
       before do
+        # Ensure to reset the memorized helper
+        described_class.instance_variable_set :@strategy_class, nil
         allow(CodeOcean::Config).to receive(:new).with(:code_ocean).and_return(codeocean_config)
         allow(codeocean_config).to receive(:read).and_return(runner_management_config)
       end
 
-      after do
-        # Reset the memorized helper
-        described_class.remove_instance_variable :@strategy_class
-      end
-
       it "uses #{strategy_class} as strategy class for constant #{strategy}" do
         expect(described_class.strategy_class).to eq(strategy_class)
       end