input: Write a function to generate a random number between 0 and 9 and return it. If the function is called without any input, it should return the generated random number.
  assert generate_random_num()==any of the numbers from 0 to 9
  assert generate_random_num()==any of the numbers from 0 to 9
  assert generate_random_num()==any of the numbers from 0 to 9
  assert generate_random_num()==any of the numbers from 0 to 9
  assert generate_random_num()==any of the numbers from 0 to 9
output: import random
  
  def generate_random_num():
      return random.randint(0, 9)