Add more must_use attributes (#2846)

… so people get a warning when they accidentally add a semicolon after the response expression in a handler function.

Also update changelogs of axum-core, axum-extra.

axum-core/src/response/mod.rs

@@ -117,6 +117,7 @@ where
 ///
 /// See [`Result`] for more details.
 #[derive(Debug)]
+#[must_use]
 pub struct ErrorResponse(Response);
 
 impl<T> From<T> for ErrorResponse