benchmarks: allow missing docs

Benchmark don't seem to benefit from being documented for a user,
so we allow missing docs for them.

Author: wprzytula

scylla-cql/benches/benchmark.rs

@@ -1,3 +1,5 @@
+#![allow(missing_docs)]
+
 use std::borrow::Cow;
 
 use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion};

scylla/benches/benchmark.rs

@@ -1,3 +1,5 @@
+#![allow(missing_docs)]
+
 use criterion::{criterion_group, criterion_main, Criterion};
 
 use bytes::BytesMut;