docs: mark v2.5.2 not released now

Author: hezhangjian

README.md

@@ -19,7 +19,7 @@ So I do not use my json-smart anymore. I had fun with this project. If you want
 
 # Changelog
 
-## *V 2.5.2* (2025-02-07)
+### *V 2.5.2* (next version)
 
 * Fix CVE-2024-57699 for predefined parsers. [PR 233](https://github.com/netplex/json-smart-v2/pull/233)