Do not share pointer_type via StgInfo clone

Co-authored-by: neonene <[email protected]>

Author: sergey-miryanov

Modules/_ctypes/stgdict.c

@@ -40,7 +40,7 @@ PyCStgInfo_clone(StgInfo *dst_info, StgInfo *src_info)
     Py_XINCREF(dst_info->converters);
     Py_XINCREF(dst_info->restype);
     Py_XINCREF(dst_info->checker);
-    Py_XINCREF(dst_info->pointer_type);
+    dst_info->pointer_type = NULL;  // the cache cannot be shared
     Py_XINCREF(dst_info->module);
 
     if (src_info->format) {