input: Write a python function to perform bubble sort on a list of integers.
  assert bubble_sort([3, 2, 5, 2, 4]) == [2, 2, 3, 4, 5]
  assert bubble_sort([5, 1, 4, 2, 8]) == [1, 2, 4, 5, 8]
  assert bubble_sort([3, 0, -1, 2, 5]) == [-1, 0, 2, 3, 5]
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