[E2E] Do not create runner resources in parallel

qa/qa/specs/features/browser_ui/4_verify/ci_project_artifacts/user_can_bulk_delete_artifacts_spec.rb

@@ -22,7 +22,7 @@ module QA
         end
 
         after do
-          Parallel.each((0..(total_runners_count - 1)), in_threads: 3) do |i|
+          Parallel.each((0..(total_runners_count - 1)), in_threads: 1) do |i|
             runners[i]&.remove_via_api!
           end
         end
@@ -45,7 +45,7 @@ module QA
       private
 
       def launch_runners
-        Parallel.each((1..total_runners_count), in_threads: 3) do |i|
+        Parallel.each((1..total_runners_count), in_threads: 1) do |i|
           runners << create(:project_runner, project: project, name: "#{executor}-#{i}", tags: [executor])
         end
       end