test: increase wait time for webhooks server to start up

spec/integration/webhooks/certificate_spec.rb

@@ -5,7 +5,7 @@
   let(:td) { TestDataBuilder.new }
   before(:all) do
     @pipe = IO.popen("bundle exec ruby spec/support/ssl_webhook_server.rb")
-    sleep 2
+    sleep 3
   end
 
   let(:webhook_request) do