Resolve clippies (#2843)

axum-core/src/ext_traits/mod.rs

@@ -30,6 +30,7 @@ mod tests {
     }
 
     // some extractor that requires the state, such as `SignedCookieJar`
+    #[allow(dead_code)]
     pub(crate) struct RequiresState(pub(crate) String);
 
     #[async_trait]

axum-core/src/lib.rs

@@ -21,7 +21,6 @@
     clippy::needless_borrow,
     clippy::match_wildcard_for_single_variants,
     clippy::if_let_mutex,
-    clippy::mismatched_target_os,
     clippy::await_holding_lock,
     clippy::match_on_vec_items,
     clippy::imprecise_flops,