input: Write a function to find the difference between consecutive numbers in a list and return a dictionary with the input number as key and the difference as value.
  assert diff_in_list([1, 2, 4, 7, 11]) == {1: 1, 2: 2, 4: 3, 7: 4}
  assert diff_in_list([10, 15, 20, 25]) == {10: 5, 15: 5, 20: 5}
  assert diff_in_list([5, 9, 12, 20]) == {5: 4, 9: 3, 12: 8}
output: def diff_in_list(lst):
      return {lst[i]: lst[i + 1] - lst[i] for i in range(len(lst) - 1)}