Implement IntoResponse for (R,) where R: IntoResponse

I just happened to notice we were missing this impl. Probably isn't the
most useful thing but still nice to have for consistency and maybe some
cursed macro stuff.

axum-core/src/response/into_response.rs

@@ -398,6 +398,16 @@ where
     }
 }
 
+impl<R> IntoResponse for (R,)
+where
+    R: IntoResponse,
+{
+    fn into_response(self) -> Response {
+        let (res,) = self;
+        res.into_response()
+    }
+}
+
 macro_rules! impl_into_response {
     ( $($ty:ident),* $(,)? ) => {
         #[allow(non_snake_case)]

axum/CHANGELOG.md

@@ -63,6 +63,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **change:** Update tokio-tungstenite to 0.19 ([#2021])
 - **change:** axum's MSRV is now 1.63 ([#2021])
 - **added:** Implement `Handler` for `T: IntoResponse` ([#2140])
+- **added:** Implement `IntoResponse` for `(R,) where R: IntoResponse`
 
 [#2021]: https://github.com/tokio-rs/axum/pull/2021
 [#2014]: https://github.com/tokio-rs/axum/pull/2014