input: Write a function to extract only the phone numbers that start with '08' from a given list of phone numbers. The function should return a list of these filtered phone numbers.
  assert extract_phone_numbers(['0834567', '0945678', '07123456', '08901234', '07890123'])==['0834567', '08901234']
output: def extract_phone_numbers(phone_numbers):
      return [number for number in phone_numbers if number.startswith('08')]