[bugfix][FindPython3] Set policy 0094 to NEW.

This fixes issue #327 (closed) to find correct Python interpreter when multiple Python versions are installed.

cmake/modules/DunePythonCommonMacros.cmake

@@ -54,6 +54,11 @@
 #
 include_guard(GLOBAL)
 
+# switches ``Python3_FIND_STRATEGY`` from VERSION to LOCATION which is the new default
+if(POLICY CMP0094)
+  cmake_policy(SET CMP0094 NEW)
+endif()
+
 # unless the user has defined the variable, unversioned names (like python3) are found
 # first, to match what users most probably use later on to call the executable
 if(NOT DEFINED Python3_FIND_UNVERSIONED_NAMES)