examples: detect windows and use correct file in the call_v_from_python example (#13114)

examples/call_v_from_python/test.py

@@ -1,4 +1,8 @@
 from ctypes import *
+import os
+
 so_file="./test.so"
+if os.name=="nt":
+  so_file="./test.dll"
 my_functions = CDLL(so_file)
 print(my_functions.square(10))