test(models): cover finished_at datetime cast

tests/Unit/ScheduledDatabaseBackupExecutionTest.php

@@ -0,0 +1,8 @@
+<?php
+
+use App\Models\ScheduledDatabaseBackupExecution;
+
+it('casts finished_at to a datetime', function () {
+    expect((new ScheduledDatabaseBackupExecution)->getCasts())
+        ->toHaveKey('finished_at', 'datetime');
+});