Ignore assertions_on_constants clippy lint

    warning: this assertion has a constant value
     --> tests/features.rs:6:5
      |
    6 | /     assert!(
    7 | |         !cfg!(feature = "proc-macro"),
    8 | |         "still compiled with proc_macro?"
    9 | |     );
      | |_____^
      |
      = help: consider moving this to an anonymous constant: `const _: () = { assert!(..); }`
      = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#assertions_on_constants
      = note: `-W clippy::assertions-on-constants` implied by `-W clippy::all`
      = help: to override `-W clippy::all` add `#[allow(clippy::assertions_on_constants)]`

Author: dtolnay

tests/features.rs

@@ -1,4 +1,4 @@
-#![allow(clippy::ignore_without_reason)]
+#![allow(clippy::assertions_on_constants, clippy::ignore_without_reason)]
 
 #[test]
 #[ignore]