Add a timeout to the test method pop_response (#3727)

If the server doesn't prove a response, this blocks indefinitely.

20 seconds is quite long but I don't want to make it too short

Author: Earlopain

lib/ruby_lsp/base_server.rb

@@ -103,7 +103,7 @@ def start
     # This method is only intended to be used in tests! Pops the latest response that would be sent to the client
     #: -> untyped
     def pop_response
-      @outgoing_queue.pop
+      @outgoing_queue.pop(timeout: 20) || raise("No message received from server")
     end
 
     # This method is only intended to be used in tests! Pushes a message to the incoming queue directly