docs: fix incorrect sample code

The length of a UUID is 128 bits. That is 32 chars, but typically expressed with a structure of 8-4-4-4-12 separated by hyphens.

Co-authored-by: Michal Sniatala <michal@sniatala.pl>

Author: kenjis

user_guide_src/source/libraries/validation/038.php

@@ -3,10 +3,10 @@
 // is_unique[table.field,ignore_field,ignore_value]
 
 $validation->setRules([
-    'name' => "max_length[30]|is_unique[supplier.name,uuid, {$uuid}]", // is not ok
-    'name' => "max_length[30]|is_unique[supplier.name,uuid,{$uuid} ]", // is not ok
-    'name' => "max_length[30]|is_unique[supplier.name,uuid,{$uuid}]",  // is ok
-    'name' => 'max_length[30]|is_unique[supplier.name,uuid,{uuid}]',   // is ok - see "Validation Placeholders"
+    'name' => "max_length[36]|is_unique[supplier.name,uuid, {$uuid}]", // is not ok
+    'name' => "max_length[36]|is_unique[supplier.name,uuid,{$uuid} ]", // is not ok
+    'name' => "max_length[36]|is_unique[supplier.name,uuid,{$uuid}]",  // is ok
+    'name' => 'max_length[36]|is_unique[supplier.name,uuid,{uuid}]',   // is ok - see "Validation Placeholders"
 ]);
 // Warning: If `$uuid` is a user input, be sure to validate the format of the value before using it.
 // Otherwise, it is vulnerable.