input: Write a function that prints the following output pattern:
  1
  12
  123
  1234
  12345
  The function should take no input and is expected to print the pattern directly to the console.
  assert print_pattern()==None
output: def print_pattern():
      for i in range(1, 6):
          for j in range(1, i + 1):
              print(j, end='')
          print()