tamer: benches (memchr): Add missing bench attr

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tamer/benches/memchr.rs

@@ -87,6 +87,7 @@ mod small_str {
             });
         }
 
+        #[bench]
         fn rust_contains_one_byte_mid_match(bench: &mut Bencher) {
             let strs = gen_strs(1000, "foo:bar");