Fix CMake 4.0 compatibility in jsoncppConfig.cmake.in (#1671)

CMake 4.0 has removed compatibility with policy versions below 3.5.
This change updates the minimum policy version from 3.0 to 3.5 in
`jsoncppConfig.cmake.in` to prevent a fatal configuration error when
downstream projects use `find_package(jsoncpp)` with CMake 4.0+.

jsoncppConfig.cmake.in

diff --git a/jsoncppConfig.cmake.in b/jsoncppConfig.cmake.in
index fdd9fea..35fed36 100644
--- a/jsoncppConfig.cmake.in
+++ b/jsoncppConfig.cmake.in
@@ -1,5 +1,5 @@
 cmake_policy(PUSH)
-cmake_policy(VERSION 3.0...3.26)
+cmake_policy(VERSION 3.5...3.26)
 
 @PACKAGE_INIT@