add v6.5.12 release notes (#19853) (#19935)

Co-authored-by: Grace Cai <qqzczy@126.com>

Author: ti-chi-bot

TOC.md

@@ -984,6 +984,7 @@
   - [TiDB 版本规则](/releases/versioning.md)
   - [TiDB 离线包](/binary-package.md)
   - v6.5
+    - [6.5.12](/releases/release-6.5.12.md)
     - [6.5.11](/releases/release-6.5.11.md)
     - [6.5.10](/releases/release-6.5.10.md)
     - [6.5.9](/releases/release-6.5.9.md)