fix: Fix always true condition

Signed-off-by: Joas Schilling <coding@schilljs.com>

Author: nickvergessen

lib/BackgroundJob/RetentionJob.php

@@ -103,7 +103,7 @@ public function run($argument): void {
 
 		$offset = '';
 		$limit = 1000;
-		while ($offset !== null) {
+		while (true) {
 			$fileIds = $this->tagMapper->getObjectIdsForTags((string)$tag, 'files', $limit, $offset);
 			$this->logger->debug('Checking retention for ' . count($fileIds) . ' files in this chunk');