Use NEW behaviour for project VERSION variables.

cf https://cmake.org/cmake/help/latest/policy/CMP0048.html#policy:CMP0048

cmake/CMakeLists.txt

diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index 1578fb8..bf3f886 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -8,6 +8,10 @@
 # CMake policies
 cmake_policy(SET CMP0022 NEW)
 
+if(POLICY CMP0048)
+  cmake_policy(SET CMP0048 NEW)
+endif()
+
 # Project
 project(protobuf C CXX)