Run cargo clippy --fix to fix CI (#2568)

… and allow one lint.

axum/src/extension.rs

@@ -87,8 +87,7 @@ where
                     "Extension of type `{}` was not found. Perhaps you forgot to add it? See `axum::Extension`.",
                     std::any::type_name::<T>()
                 ))
-            })
-            .map(|x| x.clone())?;
+            }).cloned()?;
 
         Ok(Extension(value))
     }

axum/src/test_helpers/mod.rs

@@ -10,4 +10,5 @@ pub(crate) mod tracing_helpers;
 pub(crate) fn assert_send<T: Send>() {}
 pub(crate) fn assert_sync<T: Sync>() {}
 
+#[allow(dead_code)]
 pub(crate) struct NotSendSync(*const ());