nested rpit allows capturing illegal lifetimes

[aliemjay]

The following compiles on the current nightly (1.67.0-nightly (2022-12-03 2341517)) although it shouldn't:

fn test<'s: 's>(s: &'s str) -> impl std::future::Future<Output = impl Sized> {
    async move { let _s = s; }
}

It is correctly rejected by the current beta: 1.66.0-beta.2 (2022-11-20 0040709).

This is most likely #103491 (I haven't bisected though!). Cc @cjgillot.

@rustbot label C-bug T-compiler I-unsound regression-from-stable-to-nightly A-impl-trait

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-high