week_of_month seems to be broken

[sffc]

I added a test in week_of as follows:

    // The 1st is a Monday and the week starts on Sundays.
    assert_eq!(
        simple_week_of(IsoWeekday::Sunday, 26, IsoWeekday::Friday),
        4
    );

but it returns week 1 instead of 4.

[sffc]

CC @mildgravitas, can you take a look at this?

[sffc]

CC @robertbastian -- please triage this.

[robertbastian]

@Manishearth could you take a look?

[Manishearth]

I don't really understand the week_of code! (I did not write it, nor was I the primary reviewer)

I could but it would take a while.

[Manishearth]

Having a look.

The bug is that this is wrong

https://github.com/unicode-org/icu4x/blob/d686c87ad094f9750f5cf6e42e2287076e590de9/components/calendar/src/week_of.rs#L323-L324