Fix flaky work items spec
What does this MR do and why?
This spec occasionally failed because it assumed the page was fully loaded, but often times it was blank. Fix this by looking for the CSS element that is needed in the test.
This seems to fail more often with Vite than Webpack.
Relates to #443737 (closed)
How to set up and validate locally
Run bundle exec rspec './spec/features/projects/work_items/work_item_spec.rb[1:1:12:2:1]'
many times.
Edited by Stan Hu