input: Write a python function to sort a list of integers using bubble sort.
  assert sort_integers([4, 2, 7, 1, 3, 8]) == [1, 2, 3, 4, 7, 8]
  assert sort_integers([9, 3, 5, 2, 8, 1]) == [1, 2, 3, 5, 8, 9]
  assert sort_integers([10, -1, 0, 7, 6, 3]) == [-1, 0, 3, 6, 7, 10]
output: def sort_integers(lst):
      n = len(lst)
      for i in range(n):
          for j in range(0, n-i-1):
              if lst[j] > lst[j+1]:
                  lst[j], lst[j+1] = lst[j+1], lst[j]
      return lst