fix(client): implement without_shutdown as async fn

src/client/conn/http1.rs

@@ -91,12 +91,13 @@ where
 
     /// Prevent shutdown of the underlying IO object at the end of service the request,
     /// instead run `into_parts`. This is a convenience wrapper over `poll_without_shutdown`.
-    pub fn without_shutdown(self) -> impl Future<Output = crate::Result<Parts<T>>> {
+    pub async fn without_shutdown(self) -> crate::Result<Parts<T>> {
         let mut conn = Some(self);
         futures_util::future::poll_fn(move |cx| -> Poll<crate::Result<Parts<T>>> {
             ready!(conn.as_mut().unwrap().poll_without_shutdown(cx))?;
             Poll::Ready(Ok(conn.take().unwrap().into_parts()))
         })
+        .await
     }
 }