Rustfmt doesn't fix indentation when using the let_chains feature

[FinnRG]

Playground

Minimal example:

#![feature(let_chains)]

fn main() {
    let t = Some(32);
    if true && let Some(t) = t {
            println!("Hello, World!"); // This should be changed to 4 spaces
    }
}

[FinnRG]

This will be closed with #5203.