Allow incomplete_features warnings in examples

Author: taiki-e

futures-util/src/compat/compat01as03.rs

@@ -384,6 +384,7 @@ mod io {
         ///
         /// ```
         /// #![feature(async_await, impl_trait_in_bindings)]
+        /// # #![allow(incomplete_features)]
         /// # futures::executor::block_on(async {
         /// use futures::io::AsyncReadExt;
         /// use futures_util::compat::AsyncRead01CompatExt;
@@ -413,6 +414,7 @@ mod io {
         ///
         /// ```
         /// #![feature(async_await, impl_trait_in_bindings)]
+        /// # #![allow(incomplete_features)]
         /// # futures::executor::block_on(async {
         /// use futures::io::AsyncWriteExt;
         /// use futures_util::compat::AsyncWrite01CompatExt;