Use 403 when PA licensed feature is not available

The frontend code expects the 403 HTTP response code to be returned
in order display message about the missing license or missing user
permission on the productivity analytics page.

ee/app/controllers/analytics/productivity_analytics_controller.rb

@@ -52,8 +52,8 @@ class Analytics::ProductivityAnalyticsController < Analytics::ApplicationControl
   end
 
   def check_feature_availability!
-    return render_404 unless ::License.feature_available?(:productivity_analytics)
-    return render_404 if @group && !@group.root_ancestor.feature_available?(:productivity_analytics)
+    return render_403 unless ::License.feature_available?(:productivity_analytics)
+    return render_403 if @group && !@group.root_ancestor.feature_available?(:productivity_analytics)
   end
 
   def load_group

ee/spec/controllers/analytics/productivity_analytics_controller_spec.rb

@@ -43,7 +43,7 @@ describe Analytics::ProductivityAnalyticsController do
 
       subject
 
-      expect(response).to have_gitlab_http_status(404)
+      expect(response).to have_gitlab_http_status(403)
     end
 
     it 'authorizes for ability to view analytics' do