Fix flakey user/assignee autocomplete dropdown

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/38664

This previously worked because, it would assert the correct names
in the full list and then wait for the list to go blank for the NOT assertion

Example failure, https://gitlab.com/gitlab-org/gitlab-ee/-/jobs/74649299

spec/features/issues/filtered_search/dropdown_assignee_spec.rb

@@ -79,23 +79,21 @@ describe 'Dropdown assignee', :js do
     end
 
     it 'filters by name' do
-      filtered_search.send_keys('j')
+      input_filtered_search('jac', submit: false, extra_space: false)
 
-      expect(find("#{js_dropdown_assignee} .filter-dropdown")).to have_content(user_john.name)
       expect(find("#{js_dropdown_assignee} .filter-dropdown")).to have_content(user_jacob.name)
       expect(find("#{js_dropdown_assignee} .filter-dropdown")).to have_no_content(user.name)
     end
 
     it 'filters by case insensitive name' do
-      filtered_search.send_keys('J')
+      input_filtered_search('JAC', submit: false, extra_space: false)
 
-      expect(find("#{js_dropdown_assignee} .filter-dropdown")).to have_content(user_john.name)
       expect(find("#{js_dropdown_assignee} .filter-dropdown")).to have_content(user_jacob.name)
       expect(find("#{js_dropdown_assignee} .filter-dropdown")).to have_no_content(user.name)
     end
 
     it 'filters by username with symbol' do
-      filtered_search.send_keys('@ot')
+      input_filtered_search('@ott', submit: false, extra_space: false)
 
       expect(find("#{js_dropdown_assignee} .filter-dropdown")).to have_content(user_jacob.name)
       expect(find("#{js_dropdown_assignee} .filter-dropdown")).to have_content(user.name)
@@ -103,7 +101,7 @@ describe 'Dropdown assignee', :js do
     end
 
     it 'filters by case insensitive username with symbol' do
-      filtered_search.send_keys('@OT')
+      input_filtered_search('@OTT', submit: false, extra_space: false)
 
       expect(find("#{js_dropdown_assignee} .filter-dropdown")).to have_content(user_jacob.name)
       expect(find("#{js_dropdown_assignee} .filter-dropdown")).to have_content(user.name)
@@ -111,7 +109,9 @@ describe 'Dropdown assignee', :js do
     end
 
     it 'filters by username without symbol' do
-      filtered_search.send_keys('ot')
+      filtered_search.send_keys('ott')
+
+      wait_for_requests
 
       expect(find("#{js_dropdown_assignee} .filter-dropdown")).to have_content(user_jacob.name)
       expect(find("#{js_dropdown_assignee} .filter-dropdown")).to have_content(user.name)
@@ -119,7 +119,9 @@ describe 'Dropdown assignee', :js do
     end
 
     it 'filters by case insensitive username without symbol' do
-      filtered_search.send_keys('OT')
+      filtered_search.send_keys('OTT')
+
+      wait_for_requests
 
       expect(find("#{js_dropdown_assignee} .filter-dropdown")).to have_content(user_jacob.name)
       expect(find("#{js_dropdown_assignee} .filter-dropdown")).to have_content(user.name)