fix: use raw tenant attribute to avoid type mismatch in update comparison

getTenant() casts numeric strings to int, but the no-change comparison
uses strict equality. This caused false shouldUpdate=true, triggering
authorization checks on documents with only read permissions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: abnegate

src/Database/Database.php

@@ -6055,7 +6055,7 @@ public function updateDocument(string $collection, string $id, Document $documen
             $document['$createdAt'] = ($createdAt === null || !$this->preserveDates) ? $old->getCreatedAt() : $createdAt;
 
             if ($this->adapter->getSharedTables()) {
-                $document['$tenant'] = $old->getTenant(); // Make sure user doesn't switch tenant
+                $document['$tenant'] = $old->getAttribute('$tenant'); // Make sure user doesn't switch tenant
             }
             $document = new Document($document);