Fix flaky manage_members test

What does this MR do and why?

Wait for requests before reloading the page and checking the results

Related to #384518 (closed)

Screenshots or screen recordings

N/A

How to set up and validate locally

The assumption why this test is flaky is that the underlying API could be slow sometimes. To replicate the flakiness reliably we can add sleep 10 to the API.

We also need to lift the quarantine from tests

diff --git a/ee/spec/features/groups/members/manage_members_spec.rb b/ee/spec/features/groups/members/manage_members_spec.rb
index d69da3a306c8..9de96729a365 100644
--- a/ee/spec/features/groups/members/manage_members_spec.rb
+++ b/ee/spec/features/groups/members/manage_members_spec.rb
@@ -48,7 +48,7 @@
     end
 
     shared_examples "shows an overage modal when adding one user with a given role" do |role|
-      it "shows a modal and invites them to a group if confirmed", quarantine: "https://gitlab.com/gitlab-org/gitlab/-/issues/382373" do
+      it "shows a modal and invites them to a group if confirmed" do
         group.add_owner(user1)
         add_user_by_name(user2.name, role)
 
diff --git a/lib/api/invitations.rb b/lib/api/invitations.rb
index 6aefdf146cfb..e2cff2dbd200 100644
--- a/lib/api/invitations.rb
+++ b/lib/api/invitations.rb
@@ -38,8 +38,9 @@ class Invitations < ::API::Base
           authorize_admin_source!(source_type, source)
 
           create_service_params = params.merge(source: source)
-
+          sleep 10
           ::Members::InviteService.new(current_user, create_service_params).execute
         end
 
         desc 'Get a list of group or project invitations viewable by the authenticated user' do

Now when we run we see 11 test that would fail.

bundle exec rspec ee/spec/features/groups/members/manage_members_spec.rb

When we apply wait_for_requests to shared examples and run the tests again we will only see 4 tests failing. These are the tests checking that no overage modal is shown. If we remove wait_for_all_requests (added in !104312 (merged)) from the invite_member helper all the tests will be green.

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