features [devel] update next version

docs/features/new-in-devel.md

@@ -1,6 +1,6 @@
 # Kamailio SIP Server - New Features in Devel Version
 
-**Current devel version will be numbered 5.9.0 and it is planned to be
+**Current devel version will be numbered 6.0.0 and it is planned to be
 released in late 2024 or early 2025**.
 
 **Previous devel, current stable, version was 5.8.x (released during the spring of 2024), see what was new in that release at:**