higher ranked projections: ICE -> compile change

[lcnr]

trait Trait<'a> {
    type Assoc;
}

fn foo<T: for<'a> Trait<'a>>() -> for<'a> fn(<T as Trait<'a>>::Assoc) {
    todo!()
}

fn bar<T: for<'a> Trait<'a>>() {
    let _: for<'a> fn(<_ as Trait<'a>>::Assoc) = foo::<T>();
}

This changed from an ICE on stable to compiling on beta and nightly: https://godbolt.org/z/E45bfa1d1

this shouldn't happen unintentionally and afaik we haven't added a test for this behavior either.

It would be very good to figure out which PR is responsible for this change.

[lukas-code]

searched nightlies: from nightly-2023-01-07 to nightly-2023-01-29
regressed nightly: nightly-2023-01-10
searched commit range: cc47b06...3020239
regressed commit: af58fc8 (#101947)

bisected with cargo-bisect-rustc v0.6.5

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --regress=non-ice -- check