fix mailer cache pb

@jguillaumesio fix

Author: jcheron

src/Ubiquity/mailer/MailerQueue.php

@@ -92,7 +92,7 @@ public function save($queue = true, $dequeue = true): void {
 	}
 
 	private function saveContent($part): void {
-		$content = "return " . UArray::asPhpArray($this->{$part}, 'array') . ';';
+		$content = "<?php return " . UArray::asPhpArray($this->{$part}, 'array') . ';';
 		CacheManager::$cache->store($this->rootKey . $part, $content);
 	}