changed to python 3.9 version

C++/cmake/CMakeLists.txt

@@ -207,7 +207,7 @@ cmake_minimum_required(VERSION 3.16)
 project(${module_name})
 
 # Find NGSolve and Netgen using python
-find_package(Python3 REQUIRED COMPONENTS Interpreter Development.Module)
+find_package(Python3 3.9 REQUIRED COMPONENTS Interpreter Development.Module)
 
 set(Netgen_DIR "" CACHE PATH "Path to directory containing NetgenConfig.cmake")
 set(NGSolve_DIR "" CACHE PATH "Path to directory containing NGSolveConfig.cmake")