input: Write a function to generate a random string of length 8 made of uppercase letters and numbers. The function should return the generated string.
  assert generate_random_string()=="A5B7K9L2"
  assert generate_random_string()=="X3Y8Z2Q9"
  assert generate_random_string()=="M4N6P1R5"
  assert generate_random_string()=="T2U7V3W0"
  assert generate_random_string()=="Q1R4S5T9"
output: import random
  import string
  
  def generate_random_string():
      return ''.join(random.choices(string.ascii_uppercase + string.digits, k=8))