Rename func to funk in tests to avoid Go keyword problems

Examples/test-suite/null_pointer.i

@@ -1,11 +1,9 @@
 %module null_pointer
 
-%warnfilter(SWIGWARN_PARSE_KEYWORD) func; // 'func' is a Go keyword, renamed as 'Xfunc'
-
 %inline {
   struct A {};
   
-  bool func(A* a) {
+  bool funk(A* a) {
     return !a;
   }