Fix failing test on runner spec

spec/models/clusters/applications/runner_spec.rb

@@ -41,13 +41,9 @@ describe Clusters::Applications::Runner do
 
     context 'without a runner' do
       let(:project) { create(:project) }
-      let(:cluster) { create(:cluster) }
+      let(:cluster) { create(:cluster, projects: [project]) }
       let(:gitlab_runner) { create(:clusters_applications_runner, cluster: cluster) }
 
-      before do
-        cluster.projects << project
-      end
-
       it 'creates a runner' do
         expect do
           subject