input: Write a python function to sort a list in descending order using bubble sort algorithm.
  assert sort_list([3, 4, 1, 2]) == [4, 3, 2, 1]
  assert sort_list([10, 7, 8, 5, 2]) == [10, 8, 7, 5, 2]
  assert sort_list([1, 2, 3, 4, 5]) == [5, 4, 3, 2, 1]
output: def sort_list(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