input: Write a python function to perform a bubble sort on a list.
  assert bubble_sort([4, 3, 6, 2, 8, 1, 5]) == [1, 2, 3, 4, 5, 6, 8]
  assert bubble_sort([10, 9, 8, 7, 6]) == [6, 7, 8, 9, 10]
  assert bubble_sort([1, 2, 3, 4, 5]) == [1, 2, 3, 4, 5]
output: def bubble_sort(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