`when` seemingly allows non-send/sync items

[aDotInTheVoid]

use std::rc::Rc;

use boxcars::{when, with_scheduler, Cown};

fn main() {
    with_scheduler(|| {
        let x = std::rc::Rc::new("hello");
        let y = Rc::clone(&x);
        when(&Cown::new(x), |cown| {
            dbg!(cown);
        });
        when(&Cown::new(y), |cown| {
            dbg!(cown);
        })
    })
}

compiles, but shouldnt