Diverging subexpression lint should not fire on `todo!()`

Summary

For incomplete code, it is not that helpful to point out that a subexpression diverges. I suggest suppressing the lint warning when the diverging subexpression is an application of the todo!() macro.

Lint Name

diverging_sub_expression

Reproducer

I tried this code:

#![allow(unused)]

fn main() {
  let x: u32 = todo!();
  println!("{x}");
}

I saw this happen:

warning: sub-expression diverges
 --> src/main.rs:4:16
  |
4 |   let x: u32 = todo!();
  |                ^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#diverging_sub_expression
  = note: `#[warn(clippy::diverging_sub_expression)]` on by default
  = note: this warning originates in the macro `todo` (in Nightly builds, run with -Z macro-backtrace for more info)

I expected to see this happen: No warning

Version

rustc 1.68.0-nightly (3020239de 2023-01-09)
binary: rustc
commit-hash: 3020239de947ec52677e9b4e853a6a9fc073d1f9
commit-date: 2023-01-09
host: x86_64-unknown-linux-gnu
release: 1.68.0-nightly
LLVM version: 15.0.6

Additional Labels

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