Add ClickHouse 25.8 and 26.3 LTS versions to CI matrix

https://claude.ai/code/session_01F4RsGjVD4jny3Lder5wqbc

Author: claude

.github/workflows/ci.yml

@@ -71,6 +71,8 @@ jobs:
           - "24.3"
           - "24.8"
           - "25.3"
+          - "25.8"
+          - "26.3"
         dependency-versions:
           - "highest"
     env: