input: Write a function to generate a random string of length 8 made of uppercase letters and numbers. 
  
  assert generate_random_string()=="A2Z3F4T5"
  assert generate_random_string()=="1X2Y3Z4Q"
  assert generate_random_string()=="P9L2Q8N3"
  assert generate_random_string()=="7B5C6D8E"
  assert generate_random_string()=="0K3L8M5N"
output: import random
  import string
  
  def generate_random_string():
      return ''.join(random.choices(string.ascii_uppercase + string.digits, k=8))