input: Write a python function to sort an array in ascending order using bubble sort.
  assert sort_ascending([4, 2, 7, 1, 3]) == [1, 2, 3, 4, 7]
  assert sort_ascending([10, 5, 2, 8, 6]) == [2, 5, 6, 8, 10]
  assert sort_ascending([1, 2, 3, 4, 5]) == [1, 2, 3, 4, 5]
output: def sort_ascending(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