input: Write a function to create a random string of length 8 consisting of alphabets and numbers.
  assert len(random_string_generator()) == 8
  assert all(c.isalnum() for c in random_string_generator())
  assert any(c.isdigit() for c in random_string_generator())
  assert any(c.isalpha() for c in random_string_generator())
output: import random
  import string
  
  def random_string_generator():
      characters = string.ascii_letters + string.digits
      return ''.join(random.choice(characters) for _ in range(8))