input: Write a function to print a triangle pattern of stars.
  assert print_triangle(4) == None  # Output: \n*\n**\n***\n****
  assert print_triangle(3) == None  # Output: \n*\n**\n***
  assert print_triangle(5) == None  # Output: \n*\n**\n***\n****\n*****
output: def print_triangle(n):
      for i in range(1, n + 1):
          print('*' * i)