Adjust URL in Racket 8.13 release announcement (#305)

Author: spdegabrielle

blog/_src/posts/2024-05-17-racket-v8-13.md

@@ -68,6 +68,6 @@ If you can  - please help get the word out to users and platform specific repo p
 ```
 Racket - the Language-Oriented Programming Language - version 8.13 is now available from https://download.racket-lang.org
 
-See https://racket.discourse.group/t/racket-v8-13-is-now-available/2928 for the release announcement and highlights.
+See https://blog.racket-lang.org/2024/05/racket-v8-13.html for the release announcement and highlights.
 
 ```