Ignore unused_macro_rules warning in test macros

    warning: 1st rule of macro `json_str` is never used
     --> tests/macros/mod.rs:2:5
      |
    2 |     ([]) => {
      |     ^^^^
      |
      = note: `#[warn(unused_macro_rules)]` on by default

    warning: 3rd rule of macro `json_str` is never used
      --> tests/macros/mod.rs:11:5
       |
    11 |     ({}) => {
       |     ^^^^

Author: dtolnay

tests/macros/mod.rs

@@ -1,3 +1,5 @@
+#![allow(unused_macro_rules)]
+
 macro_rules! json_str {
     ([]) => {
         "[]"