input: Write a function to search a given string in a list of strings using regex and return a message indicating whether the string matches any in the list or not.
  assert regex_search(["First", "Second", "Third"], "First") == "String matches"
  assert regex_search(["First", "Second", "Third"], "Second") == "String matches"
  assert regex_search(["First", "Second", "Third"], "Third") == "String matches"
  assert regex_search(["First", "Second", "Third"], "Fourth") == "String doesn't match"
  assert regex_search(["First", "Second", "Third"], "") == "String doesn't match"
output: import re
  
  def regex_search(string_list, search_string):
      for s in string_list:
          if re.search(search_string, s):
              return "String matches"
      return "String doesn't match"