Fix a spec failure due to the rename of Project#deployment_service to #deployment_platform

See
https://gitlab.com/gitlab-org/gitlab-ce/commit/53da3d976f3705a87edc50dca41748b5e479fc83
and https://gitlab.com/gitlab-org/gitlab-ee/-/jobs/43012757Signed-off-by: Rémy Coutable <remy@rymai.me>

app/models/environment.rb

@@ -146,7 +146,7 @@ class Environment < ActiveRecord::Base
   end
 
   def rollout_status
-    project.deployment_service.rollout_status(self) if deployment_service_ready?
+    project.deployment_platform.rollout_status(self) if deployment_service_ready?
   end
 
   def has_metrics?

spec/models/environment_spec.rb

@@ -420,7 +420,7 @@ describe Environment do
       end
 
       it 'returns the rollout status from the deployment service' do
-        expect(project.deployment_service)
+        expect(project.deployment_platform)
           .to receive(:rollout_status).with(environment)
           .and_return(:fake_rollout_status)