fn utc(_: &mut VM, mut self_val: Value, args: &Args2) -> VMResult {
    args.check_args_num(0)?;
    let time = self_val.as_mut_time();
    match time {
        TimeInfo::Local(t) => *time = TimeInfo::UTC(t.clone().into()),
        TimeInfo::UTC(_) => {}
    };
    Ok(self_val)
}
TIme#gmtime -> self
https://docs.ruby-lang.org/ja/latest/method/Time/i/gmtime.html
ruruby/src/builtin/time.rs