Wait for all Ajax and Vue requests to complete in JavaScript tests

From logs in #33756, we that it's possible for an Ajax call to be made
before the middleware receives it. To prevent stray Ajax calls from
breaking other specs, we need to wait for all scheduled calls to finish.

Closes #33756

spec/support/wait_for_requests.rb

@@ -7,7 +7,7 @@ module WaitForRequests
   def block_and_wait_for_requests_complete
     Gitlab::Testing::RequestBlockerMiddleware.block_requests!
     wait_for('pending requests complete') do
-      Gitlab::Testing::RequestBlockerMiddleware.num_active_requests.zero?
+      Gitlab::Testing::RequestBlockerMiddleware.num_active_requests.zero? && finished_all_requests?
     end
   ensure
     Gitlab::Testing::RequestBlockerMiddleware.allow_requests!