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