input: Write a function to sort a list of strings using bubble sort.
  assert bubble_sort(["cobra", "rhinoceros", "armadillo", "aardvark"]) == ["aardvark", "armadillo", "cobra", "rhinoceros"]
  assert bubble_sort(["banana", "apple", "cherry", "date"]) == ["apple", "banana", "cherry", "date"]
  assert bubble_sort(["zebra", "monkey", "elephant", "giraffe"]) == ["elephant", "giraffe", "monkey", "zebra"]
output: def bubble_sort(strings):
      n = len(strings)
      for i in range(n):
          for j in range(0, n-i-1):
              if strings[j] > strings[j+1]:
                  strings[j], strings[j+1] = strings[j+1], strings[j]
      return strings