input: Write a python function to check if two strings are equal regardless of case using regular expressions.
  assert strings_equal_ignore_case("Hello", "heLLo") == True
  assert strings_equal_ignore_case("Goodbye", "goodbye") == True
  assert strings_equal_ignore_case("Hello", "world") == False
output: def strings_equal_ignore_case(str1, str2):
      import re
      return re.match(re.escape(str1), str2, re.IGNORECASE) is not None