Made the test stage throw an error on warnings

.github/workflows/rust.yml

@@ -100,7 +100,10 @@
         },
         {
           "run": "cargo test-all-features",
-          "name": "Run `cargo test` on all features"
+          "name": "Run `cargo test` on all features",
+          "env": {
+            "RUSTFLAGS": "-D warnings"
+          }
         }
       ]
     },

src/features/impl_alloc.rs

@@ -5,7 +5,9 @@ use crate::{
     error::{DecodeError, EncodeError},
     Config,
 };
-use alloc::{borrow::Cow, boxed::Box, collections::*, rc::Rc, string::String, sync::Arc, vec::Vec};
+#[cfg(feature = "atomic")]
+use alloc::sync::Arc;
+use alloc::{borrow::Cow, boxed::Box, collections::*, rc::Rc, string::String, vec::Vec};
 
 #[derive(Default)]
 struct VecWriter {

tests/alloc.rs

@@ -7,6 +7,7 @@ mod utils;
 use alloc::borrow::Cow;
 use alloc::collections::*;
 use alloc::rc::Rc;
+#[cfg(feature = "atomic")]
 use alloc::sync::Arc;
 use utils::{the_same, the_same_with_comparer};