Incorrect week day for Hebrew calendar when ISO year is negative

[anba]

Week days are incorrect for the Hebrew calendar as soon as the corresponding ISO date has a negative year.

(Tested with release 1.4.)

use icu::calendar::Date;
use icu::calendar::types::{Era, MonthCode};
use icu::calendar::Calendar;
use icu::calendar::hebrew::Hebrew;

use std::str::FromStr;

fn main() {
  let cal = Hebrew::new_always_calculating();
  let era = Era::from_str("am").unwrap();
  let monthCode = MonthCode::from_str("M01").unwrap();

  let dt = cal.date_from_codes(era, 3760, monthCode, 1).unwrap();
  dbg!(dt);

  // Sunday, but should be Saturday per:
  // https://www.hebcal.com/converter?hd=1&hm=Tishrei&hy=3760&h2g=1
  dbg!(cal.day_of_week(&dt));

  let date_iso = cal.date_to_iso(&dt);

  dbg!(date_iso.year().number);
}

[sffc]

In Hebrew, day_of_week just calls self.date_to_iso(date).day_of_week()

The conversion to ISO returns -1-8-28, which agrees with the web site you linked. That date also returns Sunday.

I'm writing a continuity test for weekdays in ISO and am finding problems. I'll put up a PR soon.