Potential fix for flaky user_assigns_themselves_spec.rb

Introduced in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/41030, this spec
may fail if CI is slow, and the database hasn't had a chance to update.
We now wait for the request to return before checking whether the
`updated_at` column has been updated.

spec/features/merge_request/user_assigns_themselves_spec.rb

@@ -22,7 +22,12 @@ RSpec.describe 'Merge request > User assigns themselves' do
     end
 
     it 'updates updated_by', :js do
-      expect { click_button 'assign yourself' }.to change { merge_request.reload.updated_at }
+      expect do
+        click_button 'assign yourself'
+
+        expect(find('.assignee')).to have_content(user.name)
+        wait_for_all_requests
+      end.to change { merge_request.reload.updated_at }
     end
 
     it 'returns user to the merge request', :js do