input: Write a python function to validate a JSON string.
  assert validate_json_string('{"name": "John", "age": 30}') == True
  assert validate_json_string('{"name": "John", "age": 30,}') == False
  assert validate_json_string('{"name": "John", "age": "thirty"}') == True
  assert validate_json_string('{"name": "John" "age": 30}') == False
output: import json
  
  def validate_json_string(json_string):
      try:
          json.loads(json_string)
          return True
      except json.JSONDecodeError:
          return False