fix #24780 change default isolation method in dol_clone

This fixes serialization error when attempting to update a custom field value.
This change is made globally because the previous native = 0 default isolation
method is labeled as `deprecated` in the code and therefore shouldn't be used
anymore.

Signed-off-by: Alexis Thietard <alexis.thietard@rtone.fr>

htdocs/core/lib/functions.lib.php

@@ -1154,7 +1154,7 @@ function dol_buildpath($path, $type = 0, $returnemptyifnotfound = 0)
  *	@return object				Clone object
  *  @see https://php.net/manual/language.oop5.cloning.php
  */
-function dol_clone($object, $native = 0)
+function dol_clone($object, $native = 2)
 {
 	if ($native == 0) {
 		// deprecated method, use the method with native = 2 instead