Limit leaks to gitlab_transactions_stack

Reset gitlab_transactions_stack after each example to limit leaks

spec/support/cross_database_modification.rb

+# frozen_string_literal: true
+
+RSpec.configure do |config|
+  config.after do |example|
+    [::ApplicationRecord, ::Ci::ApplicationRecord].each do |base_class|
+      base_class.gitlab_transactions_stack.clear if base_class.respond_to?(:gitlab_transactions_stack)
+    end
+  end
+end