📝 Update release notes

docs/en/docs/release-notes.md

@@ -2,6 +2,7 @@
 
 ## Latest Changes
 
+* ⬆ Upgrade Starlette to `0.21.0`, including the new [`TestClient` based on HTTPX](https://github.com/encode/starlette/releases/tag/0.21.0). PR [#5471](https://github.com/tiangolo/fastapi/pull/5471) by [@pawelrubin](https://github.com/pawelrubin).
 * 🌐 Add French translation for `docs/fr/docs/advanced/additional-status-code.md`. PR [#5477](https://github.com/tiangolo/fastapi/pull/5477) by [@axel584](https://github.com/axel584).
 * 🌐 Add Portuguese translation for `docs/pt/docs/tutorial/request-forms-and-files.md`. PR [#5579](https://github.com/tiangolo/fastapi/pull/5579) by [@batlopes](https://github.com/batlopes).
 * 🌐 Add Japanese translation for `docs/ja/docs/advanced/websockets.md`. PR [#4983](https://github.com/tiangolo/fastapi/pull/4983) by [@xryuseix](https://github.com/xryuseix).