Ensure not completing finished string

Becaus of ruby/ruby#15979, closing_loc is
going to be `nil` going forward when there is not a closing
delimiter. So this predicate has to change slightly. This new
predicate will work for all prism versions.

Author: kddnewton

lib/repl_type_completor.rb

@@ -69,7 +69,7 @@ def analyze_code(code, binding = Object::TOPLEVEL_BINDING)
 
       case target_node
       when Prism::StringNode
-        return unless target_node.closing&.empty?
+        return if target_node.opening == "?" || (target_node.closing_loc && !target_node.closing.empty?)
 
         call_node, args_node = parents.last(2)
         return unless call_node.is_a?(Prism::CallNode) && call_node.receiver.nil?