input: Write a function to extract phone numbers that start with '08' from a given list. If the list is empty, return an empty list.
  assert extract_08_numbers(['0834567', '0945678', '07123456', '08901234', '07890123'])==['0834567', '08901234']
  assert extract_08_numbers([])==[]
  assert extract_08_numbers(['0934567', '07123456', '07890123'])==[]
output: def extract_08_numbers(phone_numbers):
      return [num for num in phone_numbers if num.startswith('08')]