regression: ty/closure index out of bounds ICE

[Mark-Simulacrum]

[INFO] [stderr] thread 'rustc' panicked at compiler/rustc_middle/src/ty/closure.rs:180:56:
[INFO] [stderr] index out of bounds: the len is 1 but the index is 1

https://crater-reports.s3.amazonaws.com/beta-1.73-1.2/beta-2023-09-10/reg/mononym-0.1.0/log.txt

[apiraino]

I can't reproduce with:

git clone --depth=1 https://github.com/maybevoid/mononym && cd mononym
RUSTFLAGS="--cap-lints=warn" cargo +beta-2023-09-10 test --frozen --no-run

but it does reproduces on 1.74.0-nightly (2fc85d15a 2023-09-09).

Assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-medium