input: Write a python function to merge two dictionaries.
  assert merge_dict({'a': 1, 'b': 2}, {'c': 3, 'd': 4}) == {'a': 1, 'b': 2, 'c': 3, 'd': 4}
  assert merge_dict({'key1': 'value1'}, {'key2': 'value2'}) == {'key1': 'value1', 'key2': 'value2'}
  assert merge_dict({}, {'new_key': 'new_value'}) == {'new_key': 'new_value'}
output: def merge_dict(dict1, dict2):
      merged_dict = dict1.copy()
      merged_dict.update(dict2)
      return merged_dict