Fix category of 3.6.4 to release form announcment (#1773)

Author: WojciechMazur

_posts/2025-03-07-release-notes-3.6.4.md

@@ -1,5 +1,5 @@
 ---
-category: announcement
+category: release
 permalink: /news/3.6.4/
 title: "Scala 3.6.4 is now available!"
 ---