Ignore unused_macro_rules warning in test macros

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

    warning: 1st rule of macro `hashset` is never used
      --> test_suite/tests/macros/mod.rs:27:5
       |
    27 |     () => {
       |     ^^

    warning: 1st rule of macro `hashmap` is never used
      --> test_suite/tests/macros/mod.rs:44:5
       |
    44 |     () => {
       |     ^^

    warning: 1st rule of macro `hashset` is never used
      --> test_suite/tests/macros/mod.rs:27:5
       |
    27 |     () => {
       |     ^^
       |
       = note: `#[warn(unused_macro_rules)]` on by default

test_suite/tests/macros/mod.rs

@@ -1,3 +1,5 @@
+#![allow(unused_macro_rules)]
+
 use serde_test::Token;
 use std::iter;