input: Write a python function to create a copy of a dictionary and modify a specific key's value.
  assert copy_and_modify({'key1': 'val1', 'key2': 'val2'}, 'key2', 100) == {'key1': 'val1', 'key2': 100}
  assert copy_and_modify({'a': 1, 'b': 2, 'c': 3}, 'b', 20) == {'a': 1, 'b': 20, 'c': 3}
  assert copy_and_modify({'x': 9, 'y': 8, 'z': 7}, 'x', 0) == {'x': 0, 'y': 8, 'z': 7}
output: def copy_and_modify(original_dict, key, new_value):
      new_dict = original_dict.copy()
      new_dict[key] = new_value
      return new_dict