Unmatched brace in a format string crashes the compiler

[VorfeedCanal]

Reproducer:

pub fn test(i: i32) -> String {
  format!(concat!("{0}𝖳𝖾𝗌𝗍{"), i)
}

Playground link: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=8b3a4c8413cd9d296706c9da0ac6e0c0

[compiler-errors]

I'd love to take a look at this. Seems to be ICEing in code that displays the diagnostic to fixup the actual compiler error here.

@rustbot claim