PHPORM-311 Fix Update of numeric field name

Author: GromNaN

src/Eloquent/Builder.php

@@ -309,7 +309,7 @@ protected function addUpdatedAtColumn(array $values)
         }
 
         $column = $this->model->getUpdatedAtColumn();
-        $values = array_merge(
+        $values = array_replace(
             [$column => $this->model->freshTimestampString()],
             $values,
         );

tests/Ticket/GH3335Test.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MongoDB\Laravel\Tests\Ticket;
+
+use MongoDB\Laravel\Tests\Models\Location;
+use MongoDB\Laravel\Tests\TestCase;
+
+/** @see https://github.com/mongodb/laravel-mongodb/discussions/3335 */
+class GH3335Test extends TestCase
+{
+    public function tearDown(): void
+    {
+        Location::truncate();
+
+        parent::tearDown();
+    }
+
+    public function testNumericalFieldName()
+    {
+        $model = new Location();
+        $model->id = 'foo';
+        $model->save();
+
+        $model = Location::find('foo');
+        $model->{'38'} = 'PHP';
+        $model->save();
+
+        $model = Location::find('foo');
+        self::assertSame('PHP', $model->{'38'});
+    }
+}