toml::de::Error::message returning empty string (regression from 0.5)

[ahl]

#[test]
fn has_message() {
    #[derive(Deserialize)]
    struct Config {
        thing: String,
    }

    let contents = "foo =";
    let config_parsed = toml::from_str::<Config>(contents);
    let Err(e) = config_parsed else { panic!("ok") };
    assert!(!e.message().is_empty());
}

In 0.5 there was no message() function, but Display for toml::de::Error used to report this "unexpected eof encountered at line 1 column 6"

[epage]

Related: #450