Fix deployment_platform not memoizing values in correct way

app/models/concerns/deployment_platform.rb

 module DeploymentPlatform
   # EE would override this and utilize environment argument
   def deployment_platform(environment: nil)
-    @deployment_platform ||=
+    @deployment_platform ||= {}
+    @deployment_platform[environment] ||= begin
       find_cluster_platform_kubernetes(environment: environment) ||
       find_kubernetes_service_integration ||
       build_cluster_and_deployment_platform
+    end
   end
 
-  private
-
   # EE would override this and utilize environment argument
   def find_cluster_platform_kubernetes(environment: nil)
     clusters.enabled.default_environment
       .last&.platform_kubernetes
   end
 
+  private
+
   def find_kubernetes_service_integration
     services.deployment.reorder(nil).find_by(active: true)
   end

ee/app/models/concerns/ee/deployment_platform.rb

@@ -2,15 +2,6 @@ module EE
   module DeploymentPlatform
     extend ::Gitlab::Utils::Override
 
-    override :deployment_platform
-    def deployment_platform(environment: nil)
-      find_cluster_platform_kubernetes(environment: environment) ||
-        find_kubernetes_service_integration ||
-        build_cluster_and_deployment_platform
-    end
-
-    private
-
     override :find_cluster_platform_kubernetes
     def find_cluster_platform_kubernetes(environment: nil)
       return super unless environment && feature_available?(:multiple_clusters)

spec/models/environment_spec.rb

@@ -378,7 +378,7 @@ describe Environment do
 
       shared_examples 'same behavior between KubernetesService and Platform::Kubernetes' do
         it 'returns the terminals from the deployment service' do
-          expect(project.deployment_platform)
+          expect(project.deployment_platform(environment: environment))
             .to receive(:terminals).with(environment)
             .and_return(:fake_terminals)
 
@@ -419,7 +419,7 @@ describe Environment do
         end
 
         it 'returns the rollout status from the deployment service' do
-          expect(project.deployment_platform)
+          expect(project.deployment_platform(environment: environment))
             .to receive(:rollout_status).with(environment)
             .and_return(:fake_rollout_status)