Add React Summit US 2025 and React Advanced London 2025 to conferences.md (#7761)

Add `React Summit US 2025` and `React Advanced London 2025` to the list of upcoming conferences (`conferences.md`).

Author: Hlebread

src/content/community/conferences.md

@@ -50,6 +50,16 @@ October 31 - November 01, 2025. In-person in Goa, India (hybrid event) + Oct 15
 
 [Website](https://www.reactindia.io) - [Twitter](https://twitter.com/react_india) - [Facebook](https://www.facebook.com/ReactJSIndia) - [Youtube](https://www.youtube.com/channel/UCaFbHCBkPvVv1bWs_jwYt3w)
 
+### React Summit US 2025 {/*react-summit-us-2025*/}
+November 18 - 21, 2025. In-person in New York, USA + remote (hybrid event)
+
+[Website](https://reactsummit.us/) - [Twitter](https://x.com/reactsummit)
+
+### React Advanced London 2025 {/*react-advanced-london-2025*/}
+November 28 & December 1, 2025. In-person in London, UK + online (hybrid event)
+
+[Website](https://reactadvanced.com/) - [Twitter](https://x.com/reactadvanced)
+
 
 ## Past Conferences {/*past-conferences*/}