ISO 8601 parsing from string sometimes is off by 1 nanosecond

[mati865]

Sometimes timestamps parsed from string are off by 1 nanosecond from the string text:

use time::{format_description::well_known::iso8601::Iso8601, macros::datetime, OffsetDateTime};

fn main() {
    let timestamp = "2022-07-22T12:52:50.349409+00:00";
    let parsed = OffsetDateTime::parse(timestamp, &Iso8601::DEFAULT).unwrap();
    // panic: `left` is `nanosecond: 349408999`, `right` is `nanosecond: 349409000`
    assert_eq!(parsed, datetime!(2022-07-22 12:52:50.349409000 UTC));
}

Better reproducer: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=31030fbca526a129ba26e1528bbe163a