Fix a wrong printf format.

Modules/_ctypes/_ctypes.c

@@ -1827,12 +1827,7 @@ unique_key(CDataObject *target, Py_ssize_t index)
 #if (PY_VERSION_HEX < 0x02050000)
 	cp += sprintf(cp, "%x", index);
 #else
-#ifdef MS_WIN32
-/* MSVC does not understand the 'z' size specifier */
-	cp += sprintf(cp, "%Ix", index);
-#else
-	cp += sprintf(cp, "%zx", index);
-#endif
+	cp += sprintf(cp, "%x", Py_SAFE_DOWNCAST(index, Py_ssize_t, int));
 #endif
 	while (target->b_base) {
 		bytes_left = sizeof(string) - (cp - string) - 1;