input: Write a python function to convert a dictionary to a list of tuples.
  assert dict_to_tuples({'a': 1, 'b': 2, 'c': 3}) == [('a', 1), ('b', 2), ('c', 3)]
  assert dict_to_tuples({1: 'one', 2: 'two', 3: 'three'}) == [(1, 'one'), (2, 'two'), (3, 'three')]
  assert dict_to_tuples({'x': 10, 'y': 20}) == [('x', 10), ('y', 20)]
output: def dict_to_tuples(d):
      return list(d.items())