input: Write a python function to check if a key exists in a dictionary.
  assert is_value_in_dict('a', {'a': 1, 'b': 2, 'c': 3}) == True
  assert is_value_in_dict('d', {'a': 1, 'b': 2, 'c': 3}) == False
  assert is_value_in_dict('c', {'x': 10, 'y': 20, 'c': 30}) == True
output: def is_value_in_dict(key, dictionary):
      return key in dictionary