message: docs: fix typo in "ultimate question" example snippet
  Since the formatting string is `"the answer to {} is {}.", question, answer`,
  the value of `question` should be `"the ultimate question"`, not `"the answer to..."`.
diff: //! ```
  //! # use tracing::{event, Level};
  //! # fn main() {
  -//! let question = "the answer to the ultimate question of life, the universe, and everything";
  +//! let question = "the ultimate question of life, the universe, and everything";
  //! let answer = 42;
  //! // records an event with the following fields:
  //! // - `question.answer` with the value 42,
  