Merge branch 'dm-wait-for-pipeline' into 'master'

Wait for AJAX requests to complete so they don't blow up if they are only handle…

Closes #30633

See merge request !10559

features/steps/project/merge_requests/acceptance.rb

 class Spinach::Features::ProjectMergeRequestsAcceptance < Spinach::FeatureSteps
   include LoginHelpers
   include GitlabRoutingHelper
+  include WaitForAjax
   step 'I am on the Merge Request detail page' do
     visit merge_request_path(@merge_request)
@@ -20,10 +21,18 @@ class Spinach::Features::ProjectMergeRequestsAcceptance < Spinach::FeatureSteps
   step 'I should see the Remove Source Branch button' do
     expect(page).to have_link('Remove source branch')
+
+    # Wait for AJAX requests to complete so they don't blow up if they are
+    # only handled after `DatabaseCleaner` has already run
+    wait_for_ajax
   end
   step 'I should not see the Remove Source Branch button' do
     expect(page).not_to have_link('Remove source branch')
+
+    # Wait for AJAX requests to complete so they don't blow up if they are
+    # only handled after `DatabaseCleaner` has already run
+    wait_for_ajax
   end
   step 'There is an open Merge Request' do