Fix flaky spec in user_suggests_changes_on_diff_spec.rb

The test appears to be failing occasionally because the diff notes
aren't always visible within the browser when the diff view is
reloaded. We fix this by clicking on the "Jump to first unresolved
thread" button to ensure the notes are shown.

Closes https://gitlab.com/gitlab-org/gitlab/issues/38277

spec/features/merge_request/user_suggests_changes_on_diff_spec.rb

@@ -139,6 +139,10 @@ describe 'User comments on a diff', :js do
       # Making sure it's not a Front-end cache.
       visit(diffs_project_merge_request_path(project, merge_request))
 
+      page.within '.line-resolve-all-container' do
+        page.find('.discussion-next-btn').click
+      end
+
       expect_appliable_suggestions(2)
 
       page.within("[id='#{hash}']") do