Fix flaky spec due to HTTP response order

This makes the spec wait for the unfiltered list to be rendered before
starting to search so that we're sure that the filtered response comes
after the unfiltered one.

ee/spec/features/issues/filtered_search/filter_issues_by_iteration_spec.rb

@@ -35,6 +35,10 @@ RSpec.describe 'Filter issues by iteration', :js do
         stub_licensed_features(iterations: true)
 
         visit page_path
+
+        page.has_content?(iteration_1_issue.title)
+        page.has_content?(iteration_2_issue.title)
+        page.has_content?(no_iteration_issue.title)
       end
 
       it 'filters by iteration' do