input: Write a python function to add values of two dictionaries with the same keys.
  assert add_dict_nums({'a': 1, 'b': 2}, {'a': 3, 'b': 4}) == {'a': 4, 'b': 6}
  assert add_dict_nums({'x': 10, 'y': 20}, {'x': 5, 'y': 15}) == {'x': 15, 'y': 35}
  assert add_dict_nums({'cat': 1, 'dog': 2}, {'cat': 3, 'dog': 4}) == {'cat': 4, 'dog': 6}
output: def add_dict_nums(dict1, dict2):
      return {key: dict1[key] + dict2[key] for key in dict1}