CI: Don't let warnings get away

rtic-channel/src/lib.rs

@@ -2,6 +2,7 @@
 
 #![no_std]
 #![deny(missing_docs)]
+//deny_warnings_placeholder_for_ci
 
 use core::{
     cell::UnsafeCell,

rtic-monotonics/src/lib.rs

@@ -3,6 +3,7 @@
 #![no_std]
 #![no_main]
 #![deny(missing_docs)]
+//deny_warnings_placeholder_for_ci
 #![allow(incomplete_features)]
 #![feature(async_fn_in_trait)]
 

rtic-time/src/lib.rs

@@ -2,6 +2,7 @@
 
 #![no_std]
 #![deny(missing_docs)]
+//deny_warnings_placeholder_for_ci
 #![allow(incomplete_features)]
 #![feature(async_fn_in_trait)]