Fix Environment#metrics spec

Signed-off-by: Rémy Coutable <remy@rymai.me>

spec/models/environment_spec.rb

@@ -415,7 +415,7 @@ describe Environment, models: true do
 
       it 'returns the metrics from the deployment service' do
         expect(project.monitoring_service)
-          .to receive(:metrics).with(environment)
+          .to receive(:environment_metrics).with(environment)
           .and_return(:fake_metrics)
 
         is_expected.to eq(:fake_metrics)