Ignore let_underscore_untyped pedantic clippy lint

    error: non-binding `let` without a type annotation
      --> tests/test_writedoc.rs:50:5
       |
    50 | /     let _ = writedoc! {
    51 | |         if ZERO < Pair::<fn() -> (), ()>::ONE { &mut s } else { &mut s },
    52 | |         "writedoc",
    53 | |     };
       | |______^
       |
       = help: consider adding a type annotation or removing the `let` keyword
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#let_underscore_untyped
       = note: `-D clippy::let-underscore-untyped` implied by `-D clippy::pedantic`

tests/test_writedoc.rs

@@ -1,4 +1,4 @@
-#![allow(clippy::if_same_then_else)]
+#![allow(clippy::if_same_then_else, clippy::let_underscore_untyped)]
 
 use indoc::writedoc;
 use std::fmt::Write as _;