style(storage-client): declare strict types in GcsClientFactory

Matches S3ClientFactory, which the transfer policy is ported from. The
baseline entries move again because the anonymous class shifts to line 42.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: martinsifra

src/Keboola/StorageApi/Downloader/GcsClientFactory.php

@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Keboola\StorageApi\Downloader;
 
 use Google\Auth\FetchAuthTokenInterface;