input: Write a python function to find consecutive repeated digits using regex.
  assert find_consecutive_repeated_digits("ab890087kkk") == None
  assert find_consecutive_repeated_digits("ab89888kkk") == "888"
  assert find_consecutive_repeated_digits("1234555") == "555"
output: import re
  
  def find_consecutive_repeated_digits(s):
      match = re.search(r'(\d)\1+', s)
      if match:
          return match.group(0)
      return None